Calculated from the sample figures using the displayed formula.
What is the compound interest formula?
P(1 + r/n)ⁿᵗCompound interest earns a return on the principal and on interest accumulated in earlier periods.
What do the inputs mean?
- Starting principal
- The value entered for starting principal. Keep its period and units consistent with the other inputs.
- Annual rate (%)
- The value entered for annual rate (%). Keep its period and units consistent with the other inputs.
- Years
- The value entered for years. Keep its period and units consistent with the other inputs.
- Compounds per year
- The value entered for compounds per year. Keep its period and units consistent with the other inputs.
How to calculate it step by step
- Define the decision.
Write down what the result will help you compare or decide. - Collect matching inputs.
Use figures from the same period and apply the definitions shown on this page. - Apply the formula.
P(1 + r/n)ⁿᵗ. - Check the units.
Confirm whether the result is a currency amount, percentage, number of periods or ratio. - Test a second case.
Change one assumption at a time to see what drives the result.
Worked example
Using the sample figures in the calculator, the result is $18,193.97. Change one figure at a time and recalculate to see which assumption has the greatest effect. A spreadsheet should return the same result when it uses the same formula, units and timing.
When should you use compound interest formula?
Use it to compare balances under a stated rate, term and compounding frequency.
Limitations and common mistakes
A constant rate is an assumption, not a forecast of investment performance.
Do not mix annual figures with monthly figures, ending balances with averages, or percentages with whole numbers. Record the definition used so another person can reproduce the result.
Frequently asked questions
What is compound interest formula?
Compound interest earns a return on the principal and on interest accumulated in earlier periods.
How should I use compound interest formula?
Use the formula only after matching every input to the same period, unit and definition. Then compare the result with a worked example and the decision you are trying to make.
What is the most common mistake with compound interest formula?
A constant rate is an assumption, not a forecast of investment performance.
Can I calculate compound interest formula in a spreadsheet?
Yes. Reproduce the displayed equation with separate cells for each input, keep percentages as decimals, and test the spreadsheet against the worked example before replacing the sample figures.
Sources and methodology
This page uses the Investor.gov Compound Interest Calculator for the underlying financial or reporting context. Spreadsheet-related behavior is checked against Microsoft’s financial-function documentation. Examples are illustrative and use the formula displayed on the page.