Compound Interest Calculator
See how an amount grows over time with compound interest, including optional regular contributions.
| Initial amount | |
| Monthly contribution | |
| Annual interest rate | % |
| Years | |
| Compound frequency |
Result
Your growth estimate will appear here.
Compound interest
Compound interest means you earn interest on both your original amount and on previously earned interest. More frequent compounding and regular contributions can increase the total over time.
How it works
Compound interest means you earn (or owe) interest on both the original amount and any interest added before it. Compounding more often or for longer makes growth faster.
Formula
- A = P × (1 + r/n)n×t for a lump sum (P principal, r annual rate as a decimal, n compounding periods per year, t years).
- Interest earned = A − P (adjusted for any contributions if used).
Worked example
$1,000 at 5% compounded monthly for 10 years: A = 1000 × (1 + 0.05/12)120 ≈ $1,647.01.
Assumptions
- Assumes a fixed rate and the schedule you enter. Taxes, fees, and inflation are not included and actual returns vary.
This is an estimate for general information only. Actual returns vary and are not guaranteed.
How to use the Compound Interest Calculator
It takes a few seconds, and every figure is calculated in your browser.
- Enter the initial amount.
- Enter the monthly contribution.
- Enter the annual interest rate.
- Enter the number of years.
- Choose how often interest compounds.
- Press Calculate — the result appears in the dark panel beside the form.
- Use Copy, CSV, Share or Print under the result if you want to keep it.
Compound Interest Calculator — frequently asked questions
What formula does the Compound Interest Calculator use?
A = P × (1 + r/n) n×t for a lump sum (P principal, r annual rate as a decimal, n compounding periods per year, t years). Interest earned = A − P (adjusted for any contributions if used).
How does the Compound Interest Calculator work?
Compound interest means you earn (or owe) interest on both the original amount and any interest added before it. Compounding more often or for longer makes growth faster.
What assumptions and limitations should I know about?
Assumes a fixed rate and the schedule you enter. Taxes, fees, and inflation are not included and actual returns vary.
Can you walk through a worked example?
$1,000 at 5% compounded monthly for 10 years: A = 1000 × (1 + 0.05/12) 120 ≈ $1,647.01.
Last updated 10 November 2026 · Formula, worked example and assumptions are documented above, and every result is calculated in your browser.