Compound Interest Calculator Guide: Formula & Worked Example
Short answer
Growth of savings with compounding and monthly contributions. In the fixed example below, final balance is 54,713.58. Your answer depends on the inputs and assumptions you choose.
Formula
A = P(1 + r/n)^(nt) + contributions
Use the relationship above with consistent units. The inputs are initial amount, monthly contribution, interest rate, years, compounding. Use the input scale shown beside each field and keep time periods and units consistent. Only round the final result for display.
Worked example
- Initial amount
- 10000
- Monthly contribution
- 200
- Interest rate
- 7
- Years
- 10
- Compounding
- 12
- Final balance: 54,713.58
- Total contributions: 34,000.00
- Total interest earned: 20,713.58
- Effective annual rate: 7.229%
Understanding the result
Growth of savings with compounding and monthly contributions. Start with the base example, then replace each value with the figure that matches your situation.
Initial amount
The example uses 10000 for initial amount. This is an illustration, not a recommended value. Keep the unit and time period shown by the field.
Monthly contribution
The example uses 200 for monthly contribution. This is an illustration, not a recommended value. Keep the unit and time period shown by the field.
Interest rate
The example uses 7 % / yr for interest rate. This is an illustration, not a recommended value. Keep the unit and time period shown by the field.
Years
The example uses 10 for years. This is an illustration, not a recommended value. Keep the unit and time period shown by the field.
Compounding
The example uses Monthly for compounding. This is an illustration, not a recommended value. Keep the unit and time period shown by the field.
What the comparison means
The comparison changes only initial amount, keeping every other example input fixed. This isolates that input's effect on the primary result. It does not predict future outcomes.
Rates, fees, eligibility, local tax rules and provider rounding can change the final amount. Reference tax and exchange-rate data may be outdated; verify the official source before deciding.
Comparison
| Scenario | Input | Result |
|---|---|---|
| Lower input | Initial amount: 8000 | Final balance: 50,694.25 |
| Base example | Initial amount: 10000 | Final balance: 54,713.58 |
| Higher input | Initial amount: 12000 | Final balance: 58,732.90 |
Common mistakes
- Using the wrong units for initial amount.
- Comparing results while changing more than one input at a time.
- Rates, fees, eligibility, local tax rules and provider rounding can change the final amount. Reference tax and exchange-rate data may be outdated; verify the official source before deciding.
Checklist
- Confirm initial amount.
- Confirm monthly contribution.
- Confirm interest rate is expressed in % / yr.
- Confirm years.
- Confirm compounding.
- Check the result against your source or provider.
Calculators Percentage Editorial Team
Calculator guides from the Calculators Percentage team. These introductory examples are educational, not professional advice.
Last reviewed:
Rates, fees, eligibility, local tax rules and provider rounding can change the final amount. Reference tax and exchange-rate data may be outdated; verify the official source before deciding.