Compound Interest Calculator With monthly contributions, daily to continuous compounding, and a savings goal planner
See exactly how your money grows when interest earns interest. Add regular deposits, choose how often interest compounds, and get your future balance, total interest, APY and the value in today’s money. Or set a target and find out how much to save each month to reach it.
Results match Excel’s FV function to the cent and the SEC’s Investor.gov calculator. APY follows the federal Truth in Savings (Regulation DD) formula.
Your savings plan
See your future balance. Results update as you type.
Interest and time
Your balance could grow to
$0
Calculating.
Where your balance comes from
Your deposits compared with the interest they earned.
Compound interest vs. simple interest
The gap between the green and amber lines is interest earned on interest.
How compounding frequency changes your result
Same deposits and rate, different compounding schedules.
| Compounding | APY | Final balance | Versus annual |
|---|
What would grow your money faster
Each change tested on its own against your plan.
Compound interest schedule, year by year
Key years shown.
| Year | Total deposits | Interest that year | Total interest | Balance |
|---|
Insights for your savings
What the numbers are telling you.
Key takeaways
- Compound interest is interest earned on your deposits plus all the interest they have already earned.
- The formula is A = P(1 + r/n)nt. At 7%, $10,000 grows to about $38,700 in 20 years with annual compounding.
- Time is the strongest lever. Starting 10 years earlier can more than double your final balance.
- Your interest rate matters far more than compounding frequency. Daily compounding adds very little over monthly.
- Compare savings accounts by APY, which already includes the effect of compounding.
What is compound interest?
Compound interest is interest calculated on both your original deposit and the interest it has already earned. Each period, earned interest is added to your balance, so the next round of interest is paid on a larger amount. Over time this “interest on interest” makes savings grow exponentially rather than in a straight line.
A simple example shows why it matters. Put $1,000 in an account paying 10% a year. In year one you earn $100. In year two you earn $110, because the interest from year one is now earning too. By year ten you earn about $236 in that single year, and your balance is $2,594. With simple interest, which pays only on the original $1,000, you would have $2,000.
I built this compound interest calculator as the cornerstone of the DexoCalc investment and wealth building tools. It handles everything the leading calculators do, including any compounding schedule, regular contributions, deposits at the start or end of a period and yearly increases. It also covers what most leave out: taxes on interest, inflation, a side-by-side comparison with simple interest, and a goal planner that tells you how much to save.
How to use this compound interest calculator
- Pick a mode. Choose Grow my savings to see a future balance, or Reach a savings goal to find the deposit you need.
- Enter your initial deposit and regular contribution. Choose how often you add money, from weekly to yearly.
- Add the interest rate and compounding schedule. Use the rate your bank or investment quotes. Savings accounts usually compound daily or monthly.
- Set the time frame in years and months.
- Open Advanced options if you need them. Here you can deposit at the start of each period, raise deposits each year, account for tax on interest, and change the inflation rate.
The compound interest formula
Every compound interest calculation starts from one formula. Once you see what each letter means, you can check any result by hand.
A = P × (1 + r/n)n × tFuture value of a single deposit
FV = P(1 + r/n)nt + PMT × [((1 + r/n)nt − 1) ÷ (r/n)]With a regular deposit (PMT) made each compounding period
A = P × er × tContinuous compounding
Worked example: calculating compound interest by hand
Say you invest $10,000 at 7% compounded monthly for 5 years. Here are the steps.
- Divide the rate by the compounding periods: 0.07 ÷ 12 = 0.0058333.
- Add 1: 1.0058333.
- Multiply periods per year by years: 12 × 5 = 60.
- Raise to that power: 1.005833360 = 1.4176.
- Multiply by the principal: $10,000 × 1.4176 = $14,176.25. The compound interest earned is $4,176.25.
When your deposits happen on a different schedule from compounding, for example weekly deposits into an account that compounds monthly, the calculator converts the rate to an equivalent rate per deposit period so every dollar earns interest for exactly the time it is invested.
How to calculate compound interest in Excel or Google Sheets
Spreadsheets use the FV (future value) function. Enter cash you pay in as negative numbers. For $10,000 plus $500 a month at 7% compounded monthly for 20 years:
=FV(7%/12, 20*12, -500, -10000) → $300,850.72
That is exactly what this calculator returns for the same inputs. For a single deposit with no contributions, you can also type the formula directly:
=10000*(1+7%/12)^(12*20) → $40,387.39
Add a fifth argument of 1 to the FV function, as in =FV(7%/12, 240, -500, -10000, 1), when deposits are made at the start of each month. Microsoft documents the full syntax in its FV function guide.
Compound interest vs. simple interest
Simple interest pays only on the original principal. Compound interest pays on the principal plus accumulated interest. The difference is small at first and enormous later. Here is $10,000 at 7% with annual compounding and no further deposits.
| Years | Simple interest balance | Compound interest balance | Extra from compounding |
|---|---|---|---|
| 10 years | $17,000 | $19,672 | $2,672 |
| 20 years | $24,000 | $38,697 | $14,697 |
| 30 years | $31,000 | $76,123 | $45,123 |
After 30 years, compounding produces more than twice the interest of simple interest on the very same deposit. Simple interest is mostly found on some short-term loans and bonds that pay out their interest. Savings accounts, CDs and reinvested investments compound.
Daily vs. monthly vs. annual compounding
The more often interest compounds, the sooner it starts earning its own interest. But the benefit shrinks quickly as frequency rises. This is $10,000 at 5% for 10 years.
| Compounding | APY | Balance after 10 years | Gain over annual |
|---|---|---|---|
| Annually | 5.000% | $16,288.95 | – |
| Semi-annually | 5.063% | $16,386.16 | $97.21 |
| Quarterly | 5.095% | $16,436.19 | $147.24 |
| Monthly | 5.116% | $16,470.09 | $181.14 |
| Daily | 5.127% | $16,486.65 | $197.70 |
| Continuously | 5.127% | $16,487.21 | $198.26 |
Moving from monthly to daily compounding adds only about $17 here. A higher rate matters far more: the same $10,000 at 5.5% compounded annually reaches $17,081, beating 5% compounded daily by almost $600. When choosing an account, chase the rate, not the compounding schedule.
APY vs. APR: which number should you compare?
The interest rate, sometimes called the nominal rate or APR on savings products, is the yearly rate before compounding. The annual percentage yield, or APY, is what you actually earn in a year once compounding is included. In the U.S., the Truth in Savings Act and its Regulation DD require banks and credit unions to disclose APY so you can compare accounts fairly.
APY = (1 + r/n)n − 1For continuous compounding, APY = er − 1
A 7% rate compounded monthly gives an APY of 7.229%. If one bank quotes a rate and another quotes an APY, convert both to APY before comparing. The calculator shows your APY automatically. On loans and credit cards the logic runs the other way: the APR you see understates what compounding actually costs you.
How much will my money grow with monthly contributions?
Regular deposits are where compound interest does its best work. The table shows balances from monthly contributions alone, starting from zero, at 7% compounded monthly.
| Monthly deposit | After 10 years | After 20 years | After 30 years |
|---|---|---|---|
| $100 | $17,308 | $52,093 | $121,997 |
| $250 | $43,271 | $130,232 | $304,993 |
| $500 | $86,542 | $260,463 | $609,985 |
| $1,000 | $173,085 | $520,927 | $1,219,971 |
Look at the $500 row. Over 30 years you deposit $180,000, and compound interest adds about $430,000 more. In the later years, interest earns more each year than you deposit.
The cost of waiting to start
Because compounding rewards time above everything else, the age you start saving changes the outcome more than almost any other choice. Here are three savers who each invest $300 a month at 7% until age 65.
| Starts at | Total deposited | Interest earned | Balance at 65 |
|---|---|---|---|
| Age 25 | $144,000 | $643,444 | $787,444 |
| Age 35 | $108,000 | $257,991 | $365,991 |
| Age 45 | $72,000 | $84,278 | $156,278 |
The 25-year-old deposits only $36,000 more than the 35-year-old but finishes with more than twice as much. Those first 10 years of compounding are worth over $420,000. If you are planning for retirement, the Retirement Nest Egg Calculator shows how much you need by your target age.
The Rule of 72: how long until your money doubles?
Divide 72 by your annual interest rate to estimate how many years it takes to double your money. It is a quick mental shortcut, and it is remarkably close to the exact answer for typical rates.
| Interest rate | Rule of 72 estimate | Exact doubling time |
|---|---|---|
| 2% | 36.0 years | 35.0 years |
| 4% | 18.0 years | 17.7 years |
| 6% | 12.0 years | 11.9 years |
| 8% | 9.0 years | 9.0 years |
| 10% | 7.2 years | 7.3 years |
| 12% | 6.0 years | 6.1 years |
Where compound interest works for you, and against you
High-yield savings accounts and money market accounts
These usually compound daily and credit interest monthly. Rates change with the economy, so your future earnings can rise or fall. Deposits at FDIC-insured banks are protected up to the federal insurance limit, which makes these accounts a safe home for emergency funds and short-term goals.
Certificates of deposit (CDs)
A CD locks in a fixed rate for a set term, typically from a few months to five years, so the compounding is predictable. Withdrawing early usually costs a penalty.
Bonds, stock funds and dividend reinvestment
Investments do not pay a fixed interest rate, but reinvesting their returns compounds in exactly the same way. Use an expected average return as your rate and remember that real returns vary year to year. To see how reinvested dividends add shares, try the Dividend Reinvestment (DRIP) Calculator. To check the return an existing investment has actually delivered, use the Investment Return (ROI) Calculator.
Credit cards and debt
Compound interest works against you when you borrow. Most credit cards compound daily, so an unpaid balance grows on itself the same way savings do. Paying off high-interest debt is effectively a guaranteed return equal to the interest rate you stop paying.
How inflation and taxes affect compound interest
A balance of $300,000 in 20 years will not buy what $300,000 buys today. At 3% inflation, it buys about what $166,600 does now. The calculator shows this “today’s money” figure next to every result so you can plan with real purchasing power.
Taxes slow compounding too, because tax paid each year on interest leaves less to keep growing. Interest from a regular savings account is taxed as ordinary income in the U.S. Holding long-term savings in tax-advantaged accounts such as a 401(k), IRA, Roth IRA or a UK ISA lets the full amount compound. Set a tax rate in Advanced options to see the difference for your plan.
Worked example using the default inputs
Start with $10,000, add $500 at the end of every month, and earn 7% compounded monthly for 20 years with no tax.
- Total deposits: $130,000
- Compound interest earned: $170,851
- Final balance: $300,850.72
- Simple interest balance for comparison: about $227,650
- APY: 7.229%
- In today’s money at 3% inflation: about $166,574
More than half the final balance is interest, and by year 17 the interest earned to date has overtaken everything deposited. Switch to Reach a savings goal and the calculator works backwards from any target, telling you the monthly deposit that gets you there.
How I verified this calculator
Accuracy is the whole point of a calculator, so every result was checked three ways before publishing. Balances with monthly deposits match Microsoft Excel’s FV function to the cent. Single-deposit results match the A = P(1 + r/n)nt formula and the SEC’s Investor.gov compound interest calculator. APY values follow the formula in Appendix A of Regulation DD, the federal rule banks use for their own APY disclosures. All tables on this page were generated by the same engine that powers the calculator, so the article and the tool always agree.
Common compound interest mistakes
Comparing interest rates instead of APY
Two accounts quoting the same rate can pay different amounts if they compound differently. APY settles it.
Using an unrealistic rate
A savings account will not pay stock market returns, and stock returns are never guaranteed. Use a rate that fits where the money will actually sit, and test a cautious version too.
Ignoring inflation
A large future number can feel reassuring until you convert it to today’s money. Always look at both.
Waiting for a bigger amount to start
Small deposits started early beat larger deposits started late, as the cost of waiting table shows. Starting with what you have now is almost always the better move.
Related investment and wealth building calculators
Compound interest is the engine behind every long-term financial goal. These tools apply it to specific decisions, and you can find more in the finance calculators hub.
Compound interest calculator FAQs
Use A = P(1 + r/n)^(nt). Divide the annual rate by the number of compounding periods, add 1, raise it to the total number of periods, and multiply by your principal. Subtract the principal to get the interest earned. $10,000 at 7% compounded monthly for 5 years grows to $14,176.25.
At 5% compounded monthly, $10,000 grows to about $16,470 in 10 years. At 7% compounded annually it reaches about $19,672, and at 10% about $25,937. Enter your own rate above for an exact figure.
At 7% compounded monthly, $500 a month grows to about $86,500 after 10 years, $260,500 after 20 years and $610,000 after 30 years, starting from zero.
Daily compounding earns slightly more, but the difference is tiny. On $10,000 at 5% for 10 years it adds about $17 over monthly compounding. A higher interest rate matters far more than the compounding schedule.
The interest rate is the yearly rate before compounding. APY is the yearly return including compounding. A 7% rate compounded monthly equals a 7.229% APY. Compare savings accounts by APY.
Simple interest is paid only on the original principal. Compound interest is paid on the principal plus interest already earned. Over 30 years at 7%, $10,000 grows to $31,000 with simple interest and $76,123 with annual compounding.
Use the FV function: =FV(rate/periods, periods*years, -payment, -principal). For $10,000 plus $500 a month at 7% monthly for 20 years, =FV(7%/12, 240, -500, -10000) returns $300,850.72.
Use the Rule of 72: divide 72 by your interest rate. At 6% money doubles in about 12 years, at 8% in about 9 years, and at 4% in about 18 years.
Switch the calculator to Reach a savings goal and enter your target, starting amount, rate and time frame. It solves for the exact deposit needed. For example, reaching $250,000 in 20 years at 7% compounded monthly from a $10,000 start takes about $402 a month.
Yes, slightly. Start-of-month deposits earn interest for one extra month each, which adds a little to the final balance. Change the timing under Advanced options to compare.
Continuous compounding is the mathematical limit of compounding infinitely often, calculated with A = Pe^(rt). It earns only a hair more than daily compounding and is mostly used in finance theory rather than bank accounts.
In the U.S., interest from savings accounts and CDs is generally taxed as ordinary income in the year it is earned, even if you leave it in the account. Tax-advantaged retirement accounts let interest compound without yearly tax.
Yes. Credit cards and many loans compound interest on what you owe, so unpaid balances grow faster over time. Paying down high-interest debt is one of the most reliable ways to improve your finances.
Yes for the inputs you enter. Results match Excel’s FV function to the cent and follow the Regulation DD APY formula. Real accounts can differ because rates change and investment returns vary, so treat projections as estimates.
Manzoor Ahmad
Manzoor builds and tests every calculator on DexoCalc by checking its formulas against published sources and hand-worked examples. This compound interest calculator was verified against Microsoft Excel’s FV function, the SEC’s Investor.gov calculator and the Regulation DD APY formula. Read more about Manzoor.
Sources and references
- U.S. Securities and Exchange Commission, Investor.gov compound interest calculator.
- Consumer Financial Protection Bureau, 12 CFR Part 1030, Truth in Savings (Regulation DD), via eCFR.
- Legal Information Institute, Cornell Law School, Appendix A to Part 1030, Annual Percentage Yield Calculation.
- Board of Governors of the Federal Reserve System, Regulation DD: Truth in Savings compliance guide.
- Microsoft Support, FV function.
- U.S. Bureau of Labor Statistics, Consumer Price Index.
This compound interest calculator provides estimates for education and planning. It assumes a constant interest rate, regular deposits on the schedule you choose, and tax deducted from interest as it is earned. Bank rates change and investment returns are not guaranteed. It is not financial, tax or legal advice.