Compound Interest Calculator
See how your money grows over time with the power of compounding
Compound Interest Formula
- A = Final amount
- P = Principal (initial investment)
- r = Annual interest rate (decimal)
- n = Compounding frequency per year
- t = Time in years
Sources & methodology
This calculator uses the standard compound-interest formula above. Results are estimates; actual investment returns are not guaranteed and may be higher or lower. Reference: Compound Interest Calculator, U.S. SEC (Investor.gov).
Guide
How it works
Compound interest means you earn interest on your interest — making your money grow exponentially over time. The more frequently it compounds, the faster it grows.
Formula: A = P(1 + r/n)^(nt)
With monthly contributions, each deposit also starts compounding — the earlier you start, the more each dollar works for you.
What is the difference between simple and compound interest?expand_more
Simple interest is calculated only on the principal. Compound interest is calculated on the principal plus accumulated interest, so it grows exponentially over time.
How do monthly contributions affect compound interest?expand_more
Each monthly contribution begins compounding immediately — so regular contributions can dramatically outpace a single lump sum over long time horizons.
How often should interest compound?expand_more
More frequent compounding means slightly more growth. Daily compounding earns a bit more than monthly, which earns more than annually — though the difference diminishes at lower rates.
What is the Rule of 72?expand_more
Divide 72 by your annual rate to estimate how many years it takes to double your money. At 8%, money doubles in approximately 9 years.
How does the PDF download work?expand_more
Click 'Download PDF' to open your browser's print dialog. Select 'Save as PDF' as the destination. The year-by-year table is included automatically in the printout.
Next steps