Compound Interest Calculator

What this calculator does

Compound interest is the effect of earning returns on earlier returns. This calculator estimates how a starting balance and regular monthly contributions could grow over time.

Formula used

The projection compounds monthly. Each month adds the regular contribution and applies one twelfth of the annual return.

How to read the result

The output is a projection, not a guarantee. Investment returns vary, cash savings rates can change and inflation affects real purchasing power.

Assumptions

• Assumes monthly compounding.
• Assumes contributions are made every month.
• Does not include tax, platform fees, inflation or variable market returns.

Sources and checks

This calculator uses a standard public formula. Where rules or thresholds can change, source links are listed on the relevant page.

Frequently asked questions