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Calculate Compound Interest and Investment Growth
The Tools Kit's free Compound Interest Calculator projects how a savings balance or investment grows when interest is earned on interest. Enter a starting amount, an annual interest rate, the number of years and an optional monthly contribution, pick how often interest compounds, and it shows the future value, how much of that you contributed, and how much came from interest.
It works as a savings calculator, an investment growth calculator, or a quick check on how much a high-yield savings account or CD could earn. Everything is calculated in your browser as you type, with no signup. For more money tools, browse the calculator collection.
How to Use the Compound Interest Calculator
- 1
Enter the initial amount
Type your starting balance or lump-sum deposit. You can leave it blank if you only plan to make monthly contributions.
- 2
Enter the annual interest rate and years
Add the yearly rate of return or APR as a percentage (for example 7) and how many years to project, up to 100. Both are required, and the rate must be above 0.
- 3
Add a monthly contribution (optional)
Enter how much you plan to add each month. The calculator spreads it evenly across the compounding periods you choose.
- 4
Choose the compounding frequency
Pick annually, semiannually, quarterly, monthly, or daily. Monthly is selected by default.
- 5
Read the results
The future value, total contributed, and total interest earned update instantly as you change any input.
A result appears once the rate and years are filled in and you have entered either a starting amount or a monthly contribution. Projections can run for up to 100 years, and a 0% rate is allowed, so you can see what your deposits alone would add up to.
The Compound Interest Formula
For a single deposit, compound interest follows A = P(1 + r/n)nt, where P is the principal, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is the number of years. The interest earned is A − P.
When you add a monthly contribution, the calculator adds the future value of those deposits: FV = P(1 + i)k + C × ((1 + i)k − 1) ÷ i, where i = r/n is the rate per period, k = n × t is the number of periods, and C is the deposit per period. Your monthly amount is converted to C = monthly × 12 ÷ n and added at the end of each period, so with quarterly compounding $100 a month becomes $300 a quarter.
Worked example: $1,000 to start plus $100 a month at 7% compounded monthly for 10 years grows to $19,318.14. You contribute $13,000 ($1,000 + 120 × $100), so $6,318.14 is interest. With annual compounding the same inputs give $18,546.89, because the $1,200 of yearly contributions is deposited as one lump sum at the end of each year.
How Compounding Frequency Changes the Result
The more often interest compounds, the sooner each bit of interest starts earning interest of its own. The table shows $10,000 at 7% for 10 years with no further deposits.
| Compounding | Periods per year | Future value | Interest earned |
|---|---|---|---|
| Annually | 1 | $19,671.51 | $9,671.51 |
| Semiannually | 2 | $19,897.89 | $9,897.89 |
| Quarterly | 4 | $20,015.97 | $10,015.97 |
| Monthly | 12 | $20,096.61 | $10,096.61 |
| Daily | 365 | $20,136.18 | $10,136.18 |
Moving from annual to monthly compounding adds about $425 here, while going from monthly to daily adds only about $40. That gap is the difference between the stated rate (APR) and the effective annual yield (APY): 7% compounded monthly is an APY of about 7.23%. For comparison, 7% simple interest on the same $10,000 reaches just $17,000. The rate and, above all, the number of years matter far more than the compounding schedule.
Monthly Contributions and the Power of Time
Regular deposits are what turn compound interest into real wealth. Starting from nothing, $200 a month at 7% compounded monthly for 30 years grows to $243,994.20. Only $72,000 of that is money you put in; the other $171,994.20 is interest. The Rule of 72 gives a quick feel for the effect: at 7%, a balance roughly doubles every 72 ÷ 7 ≈ 10 years.
If you invest a fixed amount every month in mutual funds in India, the SIP calculator models that directly in rupees. Canadians can project registered-account growth with the TFSA calculator or the RRSP calculator. Keep in mind that the future value here is in today's nominal dollars; use the inflation calculator to see how rising prices erode purchasing power over the same horizon.
Compounding also works against you on debt. A credit card balance that is not paid off grows on the same principle, which the credit card payoff calculator helps you plan around, and the loan calculator shows the full interest cost of an amortizing loan.
Common uses
- Projecting retirement or long-term savings growth with regular monthly deposits
- Estimating what a high-yield savings account or certificate of deposit will earn
- Comparing outcomes at different interest rates, time horizons or compounding schedules
- Showing how much of a final balance is your own money versus interest
- Setting a savings target and tracking progress alongside a net worth calculator
- Checking a percentage return by hand with a percentage calculator
Compound interest terms explained
| Term | What it means here |
|---|---|
| Principal | The initial amount you start with, entered in the Initial Amount field |
| Compound interest | Interest earned on the principal plus all interest already added to the balance |
| Simple interest | Interest earned on the original principal only; it grows in a straight line instead of a curve |
| Compounding frequency | How often interest is added to the balance: 1, 2, 4, 12 or 365 times a year in this calculator |
| Nominal rate / APR | The stated annual rate before compounding, which is the figure you type into the rate field |
| APY / effective annual rate | The rate actually earned over a year once compounding is included; 7% compounded monthly is an APY of about 7.23% |
| Future value | The projected balance at the end of the period, including contributions and interest |
| Total interest earned | Future value minus everything you put in, i.e. the growth that came from compounding |
The results are a mathematical projection at a constant rate, not a guarantee. Real returns vary year to year, and inflation and taxes are not deducted.
Frequently Asked Questions
Use A = P(1 + r/n)^(nt), where P is the principal, r the annual rate as a decimal, n the number of compounding periods per year, and t the number of years. $10,000 at 7% compounded annually for 10 years grows to $10,000 × 1.07^10 = $19,671.51.
Add the future value of a series of deposits to the lump-sum formula: FV = P(1 + i)^k + C × ((1 + i)^k − 1) ÷ i, where i is the rate per period, k the total number of periods and C the deposit per period. This calculator converts your monthly contribution into C = monthly × 12 ÷ n and adds it at the end of each period.
At 7% a year with no further deposits, $10,000 grows to $19,671.51 with annual compounding and $20,096.61 with monthly compounding. The same money at 7% simple interest reaches only $17,000.
Simple interest is paid on the original principal only, so the balance grows by the same amount every year. Compound interest is paid on the principal plus earlier interest, so each year the balance grows by more than the year before.
It helps, but less than the rate or the time horizon. At 7% over 10 years, $10,000 grows to $19,671.51 compounded annually, $20,015.97 quarterly, $20,096.61 monthly and $20,136.18 daily. The jump from annual to monthly is about $425; monthly to daily adds only about $40.
APR is the stated annual rate before compounding. APY is the effective rate once compounding is included, APY = (1 + APR/n)^n − 1. A 7% rate compounded monthly is an APY of about 7.23%, and compounded daily about 7.25%. Enter the stated rate (APR) in this calculator and choose the matching frequency.
A quick estimate is the Rule of 72: divide 72 by the annual rate. At 7%, money doubles in roughly 72 ÷ 7 = 10.3 years (the exact figure with annual compounding is about 10.24 years).
The monthly amount is multiplied by 12 and divided by the number of compounding periods, then added at the end of each period. With quarterly compounding a $100 monthly contribution becomes a $300 deposit each quarter; with annual compounding it becomes one $1,200 deposit at the end of each year, which earns slightly less than true monthly deposits.
Yes. Leave the initial amount blank and enter a monthly contribution. For example, $200 a month at 7% compounded monthly for 30 years grows to $243,994.20, of which $72,000 is your own money and $171,994.20 is interest.
A result appears once the rate and years are filled in and you have entered either an initial amount or a monthly contribution. A 0% rate works and simply shows no interest growth. A negative rate, amount or contribution, or more than 100 years, shows an error message under that field instead.
No. The future value is a nominal, pre-tax projection at a constant rate. Real investment returns vary from year to year, and inflation and taxes reduce what the final balance is worth in practice.
No. The calculation runs entirely in your browser, and the numbers you enter are not sent to or stored on a server. There is no signup and no usage limit.
Reviewed by Raja Jahangir · Last reviewed: October 7, 2026
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How does compound interest work?
Compound interest pays interest on both the original principal and on interest already earned, so growth accelerates over time. $10,000 at 7% compounded annually becomes $19,672 after ten years, versus $17,000 with simple interest. Compounding frequency matters: monthly compounding beats annual at the same stated rate.