What this calculator does
Find out what your money will be worth later if it earns a steady rate. A lump sum grows by compounding, which means the interest you earn starts earning interest too. Regular deposits each grow for however many periods are left after you make them. Adding the two gives your balance at the end.
The calculator handles both parts. Enter a starting amount, any payment you add each period, the yearly rate and the number of years. Then pick how many periods there are per year. Payments and compounding happen on the same schedule. You can choose whether each payment goes in at the start or end of its period.
Where it's used
Why this math matters outside the classroom:
- Lump-sum growth. A $1,000 deposit at 5% a year grows to about $1,628.89 after 10 years.
- Regular contributions. Savers add the future value of a stream of equal deposits to the growth of their starting balance.
- Timing of deposits. Deposits made at the start of each period end up larger than deposits made at the end, because each earns one more period.
- Finance classes. Students compute future values to compare saving now with saving the same total later.
Grade level and standards: Grades 11–12; Common Core State Standards for Mathematics HSA.SSE.B.4. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Enter your starting amount. Enter 0 if you're only making regular payments.
- If you like, enter a payment for each period. Choose whether you make it at the start or end of the period.
- Enter the yearly interest rate and the number of years.
- Choose the periods per year. Then read the future value, the total you put in, and the interest you earned.
What the inputs mean
- Payment each period
- A fixed amount you add every period. Leave it blank or 0 for a single lump sum.
- Years
- With payments, years × periods per year must be a whole number. Without payments, any number of years above zero works.
- Periods per year (compounding and payments)
- The number of periods per year. Interest is added and payments are made once per period. So monthly means 12 deposits and 12 rounds of interest a year.
- Payments are made at the
- End of period is called an ordinary annuity. Start of period is called an annuity due, and each payment earns one extra period of interest.
Formula and method
i = r ÷ n; N = n × years FV (starting amount) = PV × (1 + i)^N FV (payments at end) = PMT × ((1 + i)^N − 1) ÷ i FV (payments at start) = PMT × ((1 + i)^N − 1) ÷ i × (1 + i) at 0%: FV = PV + PMT × N
In the formulas, PV is your starting amount, PMT is each payment and FV is the future value. r is the yearly rate as a decimal, and n is the number of periods per year. i is the rate for each period, and N is the total number of periods. The starting amount grows for all N periods.
The payment formula is a shortcut for adding up every payment's growth. The first end-of-period payment grows for N − 1 periods, and the last one doesn't grow at all. Payments at the start of a period each get one more period of growth. That's where the extra (1 + i) comes from.
Worked example
You start with $5,000 and add $100 at the end of each month for 10 years at 6% a year, compounded monthly.
- Rate per month: 0.06 ÷ 12 = 0.005. Number of periods: 12 × 10 = 120.
- Starting amount: $5,000 × 1.005^120 ≈ $9,096.98.
- Payments: $100 × (1.005^120 − 1) ÷ 0.005 ≈ $16,387.93.
- Future value: $9,096.98 + $16,387.93 ≈ $25,484.92.
- Interest earned: $25,484.92 − $17,000 deposited ≈ $8,484.92.
Result: The account grows to about $25,484.92. If you make each deposit at the start of the month instead, it grows to about $25,566.86.
Understanding the result
The interest earned shows how much of your final balance came from growth, not from your own deposits. Over long periods, the growth can be more than you put in.
Because of compounding, small changes in the rate or the number of years make a big difference. Try a few what-ifs rather than relying on one projection.
Assumptions and limitations
- The rate stays the same, and interest is added once per period.
- Payments are all the same size and made once per period, at the timing you choose.
- Taxes, fees and inflation aren't taken out.
- No rounding is applied in the calculation.
- Real investments don't earn a steady rate; returns go up and down from year to year. So treat the result as an illustration, not a forecast.
- It doesn't handle payments that grow over time, or payments on a different schedule from the interest. For monthly deposits with a different compounding schedule, use the compound interest calculator.
- Rates below zero aren't supported.
Frequently asked questions
What is the difference between future value and compound interest?
They use the same idea. Future value is the general answer for a lump sum plus equal payments, based on the time value of money (money now can grow into more money later). Compound interest usually focuses on how one deposit grows. This calculator lets you set the payments and the compounding schedule together.
Why do start-of-period payments give a larger result?
Each deposit goes in one period earlier, so it earns one extra period of interest. Over 120 monthly deposits at 6%, that adds about $82 in the example above.
Does this account for inflation?
No. The result is in future dollars. To see it in today's buying power, use a rate with inflation already taken out. Or take the result to the inflation calculator and convert it to today's money.
Why do I get an error about whole periods?
Payments happen once per period, so the number of periods must be a whole number. For example, 2.5 years works with twice-a-year or monthly periods, but not with yearly periods.
How this calculator is checked
Method: Standard time-value-of-money formulas: FV = PV(1 + i)^N plus the future value of an ordinary annuity or annuity due. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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