Calculate compound growth

Project an opening balance plus repeat contributions under weekly, monthly, or annual compounding.

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ToolCompound Growth Calculator
Input
Output
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How it works

The annual rate is divided by the selected periods per year, then the lump sum and an ordinary annuity of end-of-period contributions compound for the rounded period count. Deposited capital is reported separately from modeled growth, and no return or contribution frequency is assumed.

Formula
future value = opening balance × (1 + period rate)ⁿ + contribution × ((1 + period rate)ⁿ − 1) ÷ period rate
  • At zero return the calculation switches to simple addition.
  • Contribution and compounding frequency are deliberately the same in this model.

Worked example

5,000 plus 200 a month for 15 years
At 6% compounded monthly
Input
											Initial amount: 5000
Contribution: 200
Frequency: monthly
Years: 15
Rate percent: 6
Output
												Future value: 70434.21
Total contributed: 36000
Total growth: 29434.21
Periods: 180

When to use this

Investment accounts, regular savings plans, and ISA forecasts compare opening capital, deposit frequency, time, and an assumed return.

Edge cases

  • At 0% growth, future value is opening balance plus contributions without the annuity denominator.
  • A duration too short to contain one selected period is rejected instead of rounding to zero periods.
  • A negative annual rate reduces the balance through compound losses while still adding each contribution.

References