What does the Compound Interest Calculator not include?

It does not predict returns. It uses the same return every year, and real years are not the same. It is not tax advice. The suggested tax rate is a starting point; the rules where you live decide. It does not include fund fees unless you take them off the return yourself. The market history comparison uses past averages. Past performance does not predict future results. It does not tell you where to invest. It shows what your numbers lead to.

How does the calculator apply the annual return?

Annual return. How much you expect your money to grow each year, as a percent. Nobody knows this number in advance. 3% is only an example to start from. You can type a negative number, down to -50%, to see what a steady yearly loss would do. The market history box, explained in Scenario 1, shows what real savings accounts and stock indices returned in the past. The calculator splits the yearly rate into 12 and adds growth every month, so another calculator that adds growth once a year may show a slightly different number for the same inputs.

Compound Interest Calculator - See Your Savings Grow

How much could your savings grow if you leave them to compound? This free compound interest calculator shows the balance in the years ahead, how much of it is growth, and what it is worth after tax and inflation.

Plan your savings growth

See what your savings could grow into over time, with or without regular contributions.

Your savings

Starting amount (optional)

Leave blank if you're starting from $0. Never pre-filled, since there's no way to know your real amount.

Monthly savings (optional)

Leave blank for no monthly savings.

How it grows

Annual return

Not sure? The market history box under your answer shows what savings accounts and stock indices returned in the past.

Years

How long you're planning to grow this money for.

Your estimate

Worth knowing: this estimate is before tax and inflation, and assumes the same return every year.

What your savings could grow to

A closer look at your numbers

A closer look at your numbers See how the money you put in and its growth make up your total over time, and how long a single deposit could take to double.

Your savings over time

Money you put in Growth

What makes up your total

How long could one deposit take to double?

Why real life may differ from your plan

Why real life may differ from your plan See what could remain after tax. This estimate applies one tax rate to your growth, once, at the end of your plan.

What you keep after tax

Estimated after-tax result

Estimated tax:

Country / Region:

This assumes you take out everything at the end and pay tax on the growth. Your real tax may differ.

Why real life may differ from your plan

Why real life may differ from your plan See what your future total could buy at today's prices. This uses the yearly inflation rate in your settings and does not take off tax.

: (before tax and inflation)

Inflation: what your money will really be worth

Buying power in today's money, before tax

Why real life may differ from your plan

Why real life may differ from your plan See how a lower yearly return changes your estimated total. Both use a steady rate, so this does not show market ups and downs.

What if the return were lower?

What if

What if Compare your current estimate with three examples. Each changes one input and keeps the other settings the same.

These are your own numbers, changed one at a time. This is not advice about what you should do.

Compound Interest Calculator: Help

What this calculator is for

Money can grow while it stays invested, and next year what it earned can earn too. That is compound interest: growth on top of growth. Returns can also be negative in some years; the calculator works with one steady rate, so keep that in mind.

In the first years the difference is small and easy to ignore. Over ten, twenty or thirty years it becomes a large part of what you end up with, sometimes the larger part.

The Compound Interest Calculator shows how that works on your own numbers. It answers one question: if you put money aside and let it grow, how much could you have after a number of years? Then it shows what is behind that number: how much you put in, how much the growth added, what tax and rising prices take, and how real markets compare. It puts the facts on the table; the decisions stay with you.

What you enter

The calculator needs four things.

Starting amount. Money you already have and want to put aside, in one go.
Monthly savings. A fixed amount you add every month.
Annual return. How much you expect your money to grow each year, as a percent. Nobody knows this number in advance. 3% is only an example to start from. You can type a negative number, down to -50%, to see what a steady yearly loss would do. The market history box, explained in Scenario 1, shows what real savings accounts and stock indices returned in the past. The calculator splits the yearly rate into 12 and adds growth every month, so another calculator that adds growth once a year may show a slightly different number for the same inputs.
Years. How long the money stays invested.

You need at least one of the two amounts. A starting amount alone works, monthly savings alone works, and both together work. With neither, there is nothing to grow, and the calculator will ask you for one.

More options, under the fields, holds one extra setting: a yearly increase to your monthly savings. The inflation rate used for "today's money" is in the country settings, which Not your country? Change it opens. Both are explained in the scenarios.

Two kinds of answer

Every calculation gives you two answers, one after the other.

Your estimate is the quick one. One sentence, one number, and it updates while you type. Under it, a bar splits the total into two colors: What you put in and What you earned. It is the answer you came for, and for many people it is enough.

On a wide screen the answer card sits beside the fields and stays in view as you scroll. On a phone it comes after the fields.

Before you have typed enough, the card shows Your answer will appear here, with a ring that counts what is done and a list of what is still needed. The ring fills and the list gets shorter as you type. The button below appears only when there is a real answer.

Above the button sits a one-line hook: it previews part of what the insights would show, and changes with your own numbers (for example, a lower return, or what the total buys in today's money). Under it sits a button: 4 things worth knowing about this number, with the words Growth, tax and inflation underneath. For this calculator the four parts are always there, whichever scenario you choose. Click it again to hide the insights.

This is the part that goes beyond the number. It opens with your result, then four parts: A closer look at your numbers (your savings year by year, where the money came from, and how long it takes to double), Why real life may differ from your plan (tax, inflation and markets), Ways to make it work (your own numbers, changed one at a time) and Your next question. It takes a few minutes to read, and those minutes can change how you read your own number. Click a part's heading to close it or open it again.

If you change a number after opening the insights, the button changes to Update my numbers. Click it to recalculate them.

Start over, under the fields, clears everything. If you click it by mistake, Undo brings your numbers back.

Your country, currency and tax

The calculator suggests a country from your browser's time zone, not from your IP address. From the country it sets your currency and a suggested tax rate on investment profit. You can change all of them.

You will see the result in a line like this, just above the fields:

If the guess is wrong, click Not your country? Change it and choose yours. You can also change the currency next to each amount. The suggested tax is a starting point, not tax advice.

The Your numbers stay private mark in the calculator's title bar is a reminder: the numbers you type are processed in your browser only. They are not received or stored. They leave your browser only if you choose to share a result.

Three scenarios, three people

There is one form, but three ways to fill it in: money you already have, money you add every month, or both. Instead of a dry tour of every box, this part follows three people, one for each way:

Scenario 1: Money you already have. Michael has $60,000 set aside and wonders how much it could grow.
Scenario 2: Saving a little every month. Emma can put aside $300 a month and wonders if it is worth it.
Scenario 3: Both together. Olivia has $10,000 and adds $500 a month for her children's college.

Open the scenario closest to your own situation. Scenario 1 explains every part of the answer, so the other two only show what is new.

Start here when you have an amount ready and want to know what it could become if you leave it alone.

Michael's question

Michael is 38 and runs a small business. He has $60,000 set aside. He wants to know how much it could grow if he leaves it invested for 20 years. His worry: needing the money in a bad month and finding it locked away or down.

What Michael enters

In Starting amount he types 60,000. He leaves Monthly savings empty. In Annual return he types 3, and in Years he types 20.

Michael's estimate

In 20 years his $60,000 could become about $109,245. The bar shows the split: $60,000 is what he put in, $49,245 is what the growth added. That is 45% of the total, from money he did not have to add.

The line under the bar matters: Worth knowing: this estimate is before tax and inflation, and assumes the same return every year. The insights explain both.

Michael's doubt: is 3% the right number?

"Why 3%? How am I supposed to know what to enter?"

Below the fields and Your estimate there is a box for exactly this question.

Curious how this compares to real market history? takes Michael's plan and runs it again with the average yearly return real investments had in the past. He opens it.

Two choices shape the comparison:

How many years of history to average: 10, 20 or 30. A longer period smooths out booms and crashes. A shorter one reflects more recent markets.
Which tracks to compare. On the left, lower risk, lower return: a savings account and US Treasury bonds. On the right, stock market indices: historically higher return, with real ups and downs along the way. You can compare up to six at a time.

Michael picks 10 years of history and two tracks, one from each side: Savings account and S&P 500.

The same $60,000, the same 20 years, two very different endings:

At the savings account average of the past 10 years, 2%, it grows to about $89,480.
At the S&P 500 average of the past 10 years, 14.8%, it grows to about $1,137,104.

Read the second number with care. The comparison applies a past average as one steady rate to every year of the plan. It does not replay the market's real good and bad years, and the last ten years were unusually strong for American stocks. Try 20 yr and 30 yr as well: the averages change, and so does the answer. The box says it plainly: this is a simulation based on historical averages, not a forecast, a guarantee, or financial advice.

What Michael takes from it is not a number to trust, but a range to think about. The return he enters is his choice. The box shows what similar choices have averaged in the past.

It also answers part of his worry. A steady rate draws a smooth line, but real investments, stocks above all, can be down in the very month he needs the money. The calculator does not test that. If he may need the money at a certain date, a lower-risk track and a lower return are the careful assumption.

What the insights show Michael

He clicks 4 things worth knowing about this number. The insights are a set of boxes, each answering one question. They come in the same order for everyone, so it is worth knowing them once.

What your savings could grow to

The first box repeats the answer: $109,245 after 20 years. Projected, not guaranteed.

A closer look at your numbers

What is behind the answer above.

Your growth over time

This box answers how does the money get there? The blue part of the chart is what Michael put in. It stays flat at $60,000, because he adds nothing. The brown part on top is what the growth added. It starts thin and gets thicker every year, because each year's growth also earns. That widening brown band is compound interest, drawn.

Where the money came from

Where the money came from splits the total into its sources: $60,000 starting amount and $49,245 growth. If you also add monthly savings, a third card shows them.

How long until your money doubles

How long until your money doubles answers a question many people ask first. At 3% a year, about 24 years. It uses the Rule of 72: divide 72 by the yearly return. A quick way to sanity-check any rate, not a precise projection. At 6%, it would be about 12 years.

Why real life may differ from your plan

Your plan uses today's numbers. In real life a few things change them, often by a lot.

Tax

Tax answers how much of this would I keep?

The number at the top is before tax. When Michael cashes out, he pays capital gains tax, but only on what his money grew by, not on what he put in. At the suggested 15% for the United States, that is about $7,387, leaving about $101,859.

The calculator uses a simple tax model: it assumes you take out everything at the end and pay tax on the growth, so your real tax may differ. It also depends on where you live, the type of account and how long you held the investment. If your rate is different, type it in the Capital gains tax assumption field and the box updates.

Inflation

Inflation answers what will this money really buy?

Prices rise, so the same money buys less. For this example the inflation rate, How much prices go up each year (inflation) in the country settings (Not your country? Change it), is set to 3% (for the United States the calculator starts with 2.95%). At 3% inflation a year, the $109,245 in 20 years will buy about what $60,486 buys today. Inflation takes about $48,759 of buying power. At a 3% return and 3% inflation, Michael's money roughly keeps its value. It grows on paper, but it does not get richer.

That is the most important thing the insights tell him: the return he enters has to beat inflation for his money to really grow. The rate can be changed any time in the country settings (Not your country? Change it), and the figure updates right away.

Markets

The calculator uses the same 3% every year. Real markets go up in some years and down in others, and bad years early hurt more than bad years later. This is a what-if with a lower steady return, not a test of real market ups and downs. The card shows what your result would be at a rate lower than yours: for Michael, $73,278 instead of $109,245 if his savings grew 1% a year. (When the return is too low to drop two points, the card instead shows what would happen if the money did not grow at all, 0% a year, never a negative rate.) It points back to the box Curious how this compares to real market history?, which shows what real markets did.

Ways to make it work

Small changes in what you do move the result. Three cards each change one thing and keep the rest. For Michael: adding $100 a month gives about $142,075, $32,830 more. Two more years give $115,992, $6,747 more. Starting with $5,000 more gives $118,349, $9,104 more. It shows you which lever matters most for your numbers. These are your own numbers, changed one at a time: not advice about what you should do.

Your next question

At the end, the page offers three next steps: the Savings Withdrawal Calculator, to see how long the money would last once you start taking it out, the FIRE Calculator, to see how much you need before you can stop working, and the Investment Fee Calculator, to see what a fund fee would cost over the years.

A yellow Please note box under it says that this is a projection, not financial advice, and to check the tax rules where you live.

Start here when you do not have a lump sum, but you can put something aside every month.

Emma's question

Emma is 29, in her first steady full-time job. She can put aside $300 a month. She wonders whether such a small amount is even worth saving, over the next 30 years.

What Emma enters

She leaves Starting amount empty. In Monthly savings she types 300. Annual return is 3, and Years is 30.

Emma's estimate

In 30 years Emma could have about $174,821. She puts in $108,000, $300 at a time. The growth adds $66,821. More than a third of her savings comes from money she never had to set aside.

The insights work as in Scenario 1. One box shows her story most clearly:

Where the money came from now shows Your monthly contributions, $108,000, and the growth, $66,821. No starting amount card, because she had none.

The Ways to make it work cards show what $100 more a month, two more years, or $5,000 at the start would add for Emma. The monthly one is the biggest: $58,274 more.

Emma's doubt: what if I save more as I earn more?

"My salary will go up. What if I add a little more every year?"

She opens More options.

The inflation rate is not in this panel. It is How much prices go up each year (inflation) in the country settings (Not your country? Change it), and it is the yearly rate used for the "today's money" figure. It starts with your country's latest yearly figure from the World Bank, shown with its year, or 2.5% when there is none. That figure is how much prices rose in that year, not a forecast.
Increase contribution each year raises the monthly amount by a percent every year, the way a raise would. Emma types 3.

Now she could have about $259,555, about $85,000 more. Most of that difference is the extra money she adds herself: $171,271 in total instead of $108,000, about $63,000 more over the years. The growth on it adds the rest: $88,283 instead of $66,821.

For Emma the answer to her question is clear: a small amount is worth saving. Her own deposits are the larger part of the result, and growth adds more than a third on top, without her lifting a finger.

Start here when you have some money already and will keep adding to it.

Olivia's question

Olivia is 45, a teacher and a mother of two. Her oldest starts college in 10 years. She has $10,000 saved and can add $500 a month. She wants to know what that could become by then.

What Olivia enters

In Starting amount she types 10,000. In Monthly savings she types 500. Annual return is 3, and Years is 10.

Olivia's estimate

In 10 years Olivia could have about $83,364. She puts in $70,000: $10,000 at the start and $500 a month. The growth adds $13,364.

Notice the split: only 16% of her total comes from growth, against 45% for Michael and 38% for Emma. The difference is time. Ten years is not long enough for compounding to do much. It is the same lesson from the other side.

Olivia's doubt: will it be enough for college?

"College costs keep going up. What will this money really buy in ten years?"

The inflation box in her insights answers that.

At 3% inflation a year, her $83,364 will buy about what $62,031 buys today. And that is before tax. This is buying power measured by prices in general, not a promise of how many years of college it will pay for.

If she thinks college costs rise faster than prices in general, she can raise How much prices go up each year (inflation) in the country settings (Not your country? Change it) and see the answer change. To see what one year of college will cost then, the Inflation Calculator answers exactly that question.

The Ways to make it work cards work the same. For her, two more years add the most, $17,500, because ten years is short.

The rest of the page

The three scenarios cover the calculator itself. The parts below explain what else the page offers. They work the same whichever scenario you chose.

Explore Your Savings Growth Plan

THE BIGGER PICTURE

What really makes your money grow

A practical look at compounding, time, and risk, and what this calculator can’t tell you.

You’ve entered a starting amount, perhaps a monthly contribution, and a growth rate. Now you’re looking at a projection for years from now. This is about what’s actually behind that number.

Your final balance comes from two sources. The first is the money you actually put in. The second is the growth that built up on top of it, including growth on growth.

Three ideas that change how you read the result

Compound interest. Interest earned is added to your balance, so it earns interest itself from then on. This calculator compounds monthly. $10,000 at a 6% annual return earns $50 in month 1 (a 0.5% monthly rate). In month 2 it earns 0.5% of $10,050, not $10,000, so the interest is already a little more than the month before.
Rule of 72. Divide 72 by your expected annual return to estimate how many years it takes your money to double. At 6%, about 12 years. It’s a rough estimate, most accurate when the rate stays steady.
Nominal vs. real value. What your balance shows on paper, and what that number can actually buy once prices have risen. $100,000 in 15 years at 3% average inflation buys roughly what $64,000 buys today.

Common situations include long-term saving, comparing starting now against waiting a few years, and estimating how a monthly-contribution habit adds up.

What drives your result

Four things move the result: your starting balance, your contributions, how long the money stays invested, and the return you assume. No single one always dominates. It depends on your own numbers.

Time affects the result in two ways: a longer plan usually means making more contributions, and your starting balance and earlier contributions have longer to compound.

A projection is not a promise

This calculator applies the return rate you entered the same way, every year. Actual investment returns vary. Some years are higher, some are lower, and some years lose money.

In real investments, pursuing a higher expected return usually means accepting more uncertainty and a greater chance of loss. A higher number typed into this calculator doesn’t create that risk by itself. It only shows the outcome if a steady rate held every year.

What the headline number leaves out

The headline number is before tax and fees. The calculator estimates capital gains tax separately, on the growth only, below the result. Fund fees are not included: if the return you entered is before fees, take the fee off it yourself.

Inflation isn’t in the main number either. Open “What this is worth in today’s money” in the results to see that adjustment separately.

Two scenarios worth trying

Compare investing for 20 years with waiting 5 years and investing for only 15 years, using the same starting amount, contribution, and return. Then lower the return by 2 percentage points and see how much of the gain that takes back.

Planning to live from your savings one day? The Savings Withdrawal Calculator shows how long they could last.

📖 Financial terms, explained

Words that appear in this calculator or on this page, in plain English.

Compound interest: Interest paid on the money you put in and on the interest already earned. Investor.gov ↗
Annual return: The yearly percentage your money is assumed to grow by. The calculator applies it the same way every year; real returns go up and down.
Contribution: The amount you add regularly, for example every month.
Rule of 72: Divide 72 by the yearly return to estimate how many years it takes money to double. At 6%, about 12 years. A rough check, not a precise projection.
Nominal value: What your balance shows on paper, before rising prices are taken into account.
Real value (today’s money): What that balance can actually buy, shown in today’s prices.
Inflation: Prices rising over time, so the same money buys less. US Bureau of Labor Statistics: CPI ↗
Capital gains tax: Tax on the growth of an investment when you sell or withdraw it, not on the money you put in. The calculator estimates it with one rate you can change. IRS: capital gains ↗
Savings account: A bank account that pays interest at a stated rate, which may be fixed or may change.
US Treasury bonds: Loans to the US government that last 20 or 30 years and pay interest every six months. TreasuryDirect ↗
Stock market index: A group of companies whose combined value is tracked as one number, used to follow part of the stock market.
S&P 500: An index of 500 leading US companies, covering about 80% of the value of the US stock market. S&P Dow Jones Indices ↗
Dow Jones Industrial Average: An index of 30 large US companies. S&P Dow Jones Indices ↗
Nasdaq-100: An index of 100 of the largest companies listed on the Nasdaq stock market. Nasdaq ↗
MSCI World: An index of large and mid-sized companies across developed countries, more than a thousand companies in all. MSCI ↗
Volatility: How much a value goes up and down. Higher volatility means bigger swings, in both directions.
Historical average: The average yearly return over a past period, for example 10, 20 or 30 years. Past results do not predict future ones.

Common questions about compound interest

What annual return should I enter?

Use a rate that matches the account or investment you’re modeling, and check whether it’s stated before or after fees. Future returns are uncertain, so try a lower and a higher scenario instead of relying on one number. A single recent year’s return is not a reliable long-term assumption.

Do savings accounts and investments compound in the same way?

Not exactly. A savings account earns interest at a stated rate, which may be fixed or variable depending on the account. An investment’s value changes with the market. When gains or income stay invested, they can compound too, but the investment can also lose value.

Why does another compound interest calculator show a different result for the same inputs?

Small differences add up. Whether contributions are assumed at the start or end of each period, how often growth compounds, and whether fees are included can all shift the result, even with the same headline numbers.

Compound Interest Calculator (Excel)

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Plan your savings growth

Interesting insights for your numbers

What your savings could grow to

A closer look at your numbers

Your savings over time

What makes up your total

How long could one deposit take to double?

Why real life may differ from your plan

What you keep after tax

Why real life may differ from your plan

Inflation: what your money will really be worth

Why real life may differ from your plan

What if the return were lower?

What if

Related calculators

Share your results

Explore Your Savings Growth Plan

What really makes your money grow

Three ideas that change how you read the result

Two scenarios worth trying

Compound Interest Calculator (Excel)