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Compound Interest Calculator

Project savings with monthly contributions, compare two interest rates and explore yearly growth.

Your calculation

USD
USD
%
years
Up to 100 years. With deposits, use whole months: 1.5 years = 18 months.

Both scenarios use the same deposits and timing. Rates are nominal annual rates, not APY. Set monthly contribution to 0 for a single starting deposit.

Result

Projected balance

$17,175.24

Starting balance
$1,000.00
Monthly deposits added
$12,000.00
Total money deposited
$13,000.00
Interest earned
$4,175.24

Fixed nonnegative rates; no withdrawals, taxes, fees or inflation. Monthly deposits use an equivalent monthly growth rate. A mathematical projection, not a guaranteed return.

How your balance grows

Scenario A separates deposits from interest. Lines connect yearly checkpoints; the table provides exact figures.

08.6K17.2KStart10 yearsUSD
  • Money deposited
  • Interest (A)
  • A: 5%

Year-by-year breakdown

Deposits include the starting balance. Interest is cumulative.

USD · End-of-month deposits · 5%
YearTotal depositedInterestBalance
Start$1,000.00$0.00$1,000.00
1$2,200.00$79.05$2,279.05
2$3,400.00$223.53$3,623.53
3$4,600.00$436.81$5,036.81
4$5,800.00$722.38$6,522.38
5$7,000.00$1,083.97$8,083.97
6$8,200.00$1,525.44$9,725.44
7$9,400.00$2,050.90$11,450.90
8$10,600.00$2,664.64$13,264.64
9$11,800.00$3,371.17$15,171.17
10$13,000.00$4,175.24$17,175.24

The starting row is before the first contribution. CSV includes calculation settings and up to six decimal places; table amounts use the selected currency’s display precision.

Calculated in your browser. Your inputs are not sent to a server.

How to use this calculator

Enter a starting balance and a fixed monthly contribution, then choose the nominal annual rate, duration and compounding frequency. Choose whether deposits arrive at the beginning or end of each month. Enable comparison to try a second rate with identical deposits. The chart separates deposited money from interest; the table and CSV show annual checkpoints and the final partial year. Set contributions to zero to model only the starting balance.

The math behind it

Monthly growth g = (1 + annual rate / 100 / frequency)^(frequency / 12)
Months m = 12 × years
End-of-month deposits: total = principal × g^m + monthly deposit × (g^m − 1) / (g − 1)
Beginning-of-month deposits: multiply the deposit term by g
At 0%: total = principal + monthly deposit × m
Interest = total − principal − total monthly deposits

A worked example

Starting with 1,000 and adding 100 at each month’s end for 10 years at 5%, compounded monthly, produces about 17,175.24. Deposited money totals 13,000 and interest is about 4,175.24. With contributions set to zero, the same starting balance grows to 1,647.01.

Assumptions & precision

Rates and deposits are fixed and nonnegative; no withdrawals, fees, taxes, inflation or investment risk. Daily means 365 compounding periods per year. Deposits remain monthly even with annual or daily compounding: an equivalent monthly rate interpolates growth between compounding dates, which can differ from actual account crediting rules. Contributions require a whole number of months; without contributions, fractional years are supported. The starting checkpoint is before any monthly deposit. Both scenarios share all inputs except rate. Duration is limited to 100 years and output magnitudes to 10¹⁵. Currency changes display only, with no exchange conversion. Calculations retain internal precision; currency amounts round for display and CSV numbers use up to six decimals. Charts connect annual checkpoints and the final partial year, not individual deposits. These are scenarios, not guaranteed investment returns.

Common questions

Is this the same as annual percentage yield?

No. This input is a nominal annual rate divided across compounding periods. APY already accounts for compounding and should not be entered as the nominal rate without conversion.

Does beginning-of-month timing earn more?

At a positive fixed rate, each deposit has one additional month to grow. The number and amount of deposits remain the same. At zero interest, both timings produce the same result.

Can I compare different monthly deposits?

The comparison changes only the rate, so the effect of that assumption is clear. To compare contribution amounts, change the monthly deposit and download each scenario separately.