About the Compound Interest Calculator
A free, instant calculator that shows how your savings or investments grow through the power of compounding.
What it is
The Compound Interest Calculator projects how a lump sum grows over time when interest is earned on both the original principal and the accumulated interest. Enter your numbers and results update instantly — no submit button, no page reload.
Everything runs in your browser. Your financial figures are never sent to a server, stored, or logged anywhere. Close the tab and the data is gone.
Key features
Adjustable compounding frequency
Choose daily, monthly, quarterly, or yearly compounding and immediately see the difference in your final balance. More frequent compounding means more interest on interest.
Regular contributions
Add a recurring monthly or yearly contribution to model a savings plan. The calculator adds each contribution at the right interval and applies compounding on top.
Year-by-year breakdown
A table showing balance, total contributions, and total interest earned at the end of each year — so you can see exactly when compound growth really starts to accelerate.
Growth chart
An SVG line chart plots your total balance against your contributions over the full investment period, making the exponential curve of compounding visually clear.
Who it's for
Retirement planners
Model a long-term investment or pension pot over 20–40 years and see how regular contributions dramatically compound the final balance.
Savers
Project a savings account, ISA, or fixed deposit to a specific target — a house deposit, emergency fund, or lump-sum goal.
Students & learners
Understand how compound interest works by changing variables and watching the numbers and chart update in real time.
Investors
Compare the impact of different annual return rates, compounding frequencies, and top-up amounts on a portfolio's future value.
How the calculation works
The calculator simulates growth month by month. For each month it applies the effective monthly interest rate derived from your chosen compounding frequency, then adds any regular contributions. This approach handles all combinations of contribution and compounding schedules accurately without rounding errors that arise from period mismatches.
Compounding frequencies are converted to an equivalent monthly rate: monthly compounding uses r/12 directly; quarterly uses (1 + r/4)1/3 − 1; daily uses (1 + r/365)365/12 − 1; yearly uses (1 + r)1/12 − 1. This ensures consistency regardless of the chosen frequency.
The results are gross projections and do not account for taxes, investment fees, or inflation. For a conservative real-terms estimate, subtract expected inflation and tax rates from the interest rate before calculating.
Completely free
No sign-up, no rate limit, no premium tier. Project 1 year or 100 years — the calculator handles both instantly. If you find it useful, sharing it with someone planning their savings is all we ask.