Compound Interest Calculator
See how a starting amount and regular monthly contributions grow over time, with the interest earned and a year-by-year table. Everything runs in your browser.
Your investment
Leave the starting amount or the monthly contribution at zero if you only need one of them. The rate is the annual rate; the tool converts it for the compounding frequency you pick.
Growth summary
Enter an amount to see how it grows.
Year-by-year growth
The table appears once the inputs are valid.
What compound interest does
Compound interest pays interest on the interest you have already earned, so a balance grows faster the longer it is left alone. A compound interest calculator turns a starting amount, a monthly contribution, a rate and a time frame into the future value of that money.
The gap between simple and compound growth is small in year one and enormous by year thirty, which is why the year-by-year table matters more than the final number on its own.
For fixed-rate monthly borrowing, use the loan calculator with extra payments to compare repayment costs and the interest saved by paying down principal.
How to calculate compound interest
- Enter the amount you are starting with, or leave it empty if you are starting from zero.
- Add a monthly contribution if you are investing regularly; you can leave this at zero for a lump sum only.
- Type the annual interest rate and the number of years.
- Pick the compounding frequency your account uses, choose whether contributions arrive at the start or the end of the month, and read the future value and the year-by-year table.
Compound interest examples
Monthly saving
$10,000 plus $200 a month at 7% for 10 years, compounded monthly
Future value $54,713.58, of which $20,713.58 is interest
Long-term investing
$500 a month at 6% for 30 years, compounded monthly
Future value $502,257.52, of which $322,257.52 is interest
Lump sum, annual compounding
$25,000 at 5% for 20 years, compounded annually
$66,332.44, with no further contributions
UrsaKit vs other compound interest calculators
| Dimension | UrsaKit | calculator.net | calculator.io | thecalculatorsite |
|---|---|---|---|---|
| Price | Free | Free with ads | Free with ads | Free with ads |
| Calculates as you type | Yes | No | Yes | Yes |
| What the page does | One growth calculation | APR / APY converter | Five modes side by side | Several calculators |
| Monthly contributions | Yes | No | No | Yes |
| Year-by-year table | Yes | No | No | Yes |
| Uploads anything | No | No | No | No |
Frequently asked questions
What is the compound interest formula?
For a lump sum it is A = P x (1 + r/n)^(nt), where r is the annual rate and n is the number of compounding periods per year. Regular contributions turn it into an annuity formula, and this tool runs the equivalent month-by-month calculation.
Does the compounding frequency really matter?
It matters, but less than most people expect. $10,000 at 5% for 20 years reaches about $26,532.98 compounded annually and about $27,180.96 compounded daily, a difference of roughly $647.98.
Should I choose monthly or yearly compounding?
Use the frequency your account actually pays. High-yield savings accounts usually compound daily or monthly, while some bonds and rough index estimates use annual compounding. The default here is monthly.
What is the difference between contributions at the start and the end of the month?
A contribution at the start of the month earns one extra month of interest, so the final balance is slightly higher. Most payroll and bank transfers arrive at the end of the month.
Can compound interest work against me?
Yes. The same maths makes debt grow, which is why a credit card charging 20% a year is so expensive. Paying it down early has the same power as investing early.
Is my data sent anywhere?
No. The amounts, rate and frequency stay in your browser and the table is generated locally.