Compound Interest Calculator
See exactly how your money grows over time, with contributions and compounding working together. Works in any currency.
Calculate Your Growth
Enter what you're starting with, adding monthly, and for how long.
What Makes Compound Interest So Powerful
Compound interest means you earn returns not just on what you put in, but on the returns you've already earned. Every year, your gains become part of the balance that earns the next year's gains. Early on, this effect is small and easy to overlook. Given enough time, it becomes the single biggest driver of growth, often outgrowing your own contributions entirely.
This is why starting early matters more than almost anything else in investing. Ten extra years of compounding can outweigh contributing significantly more money later.
How This Calculator Works
Starting amount
The lump sum you're investing today, if any.
Monthly contribution
Money added on a regular schedule compounds too. Even modest monthly amounts add up significantly over long periods.
Expected annual return
This is an estimate, not a guarantee. Markets fluctuate year to year; this calculator assumes a steady average return applied monthly for simplicity.
Years invested
Time is the single most powerful variable in this calculation. The chart above shows how the growth curve bends upward the longer money stays invested.
A Quick Example
Say you start with $5,000, add $200 a month, and earn a 7% average annual return over 20 years.
- Total you contribute: $53,000 (the starting amount plus 20 years of monthly contributions)
- Future value: roughly $112,000
- Growth from compounding: roughly $59,000, more than what you actually put in
Stretch the same plan to 30 years instead of 20, and the future value rises to well over $230,000. An extra 10 years roughly doubles the result, even though total contributions only grow by a third.
Common Mistakes People Make
- Waiting to start. Delaying by even a few years can cost more in missed growth than most people expect, since compounding needs time to build momentum.
- Assuming returns are guaranteed. Real markets go up and down year to year. The average smooths out over long periods, but any single year can look very different.
- Withdrawing early. Pulling money out resets the compounding effect on that amount and interrupts long-term growth.
- Ignoring fees. High fees on investment accounts quietly eat into your real return every single year, compounding against you instead of for you.
- Underestimating small contributions. Even $50 extra a month, invested consistently over decades, can add up to a meaningful sum.
Frequently Asked Questions
Yes. The math is currency-neutral. Enter your numbers in your own currency and the results will be in the same unit.
It depends on what you're invested in. Broad stock market index funds have historically averaged around 7% a year after inflation over long periods, but savings accounts, bonds, and individual stocks can vary widely. Try a few different rates to see a realistic range.
Not directly. If you'd rather see results in today's purchasing power, use an inflation-adjusted return rate (historically, subtracting roughly 2-3% from the nominal return is a common approach).
The math is the same principle, just with a much lower, more predictable rate for a savings account versus a more variable, typically higher rate for investments.
Once a year is plenty, or whenever your contribution amount or goals change meaningfully.
Want to go further? Read our complete guide to investing for beginners.