Compound interest calculator with regular contributions
Compound interest is interest earned on your interest. Each time it is added to the balance, the next round of interest is calculated on a slightly bigger amount, so growth accelerates over time. This compound interest calculator shows exactly how much a lump sum and regular savings could grow to, how much of the final balance is your own money and how much is interest earned.
You can choose any compounding frequency — yearly, half-yearly, quarterly, monthly, daily or continuous — add a monthly or yearly contribution paid at the start or end of each period, and set the time in years and months. A stacked bar chart and a year-by-year table show the growth, and the table downloads as CSV.
It suits savings accounts, deposits, bonds and long-term investment projections in dollars, rupees, pounds, euros or any other currency. Real returns vary and investments can lose value, so treat the results as estimates rather than financial advice.
How to use the Compound Interest Calculator
- Choose your currency, then enter the Initial investment (it can be 0 if you only make regular deposits).
- Type the Annual interest rate and pick the Compounding frequency stated by your bank or product.
- Set the Time period in years plus any extra months.
- Add a Regular contribution, choose per month or per year, and whether it is paid at the start or end of each period.
- Read the final balance, total contributions, interest earned and the effective annual rate.
- Scroll the Year-by-year growth table or press Download CSV.
Compound Interest Calculator features
Six compounding options
Yearly, half-yearly, quarterly, monthly, daily (365) and continuous compounding using eʳᵗ.
Monthly or yearly deposits
Contributions at the start (annuity due) or end (ordinary annuity) of each period.
Effective annual rate
Shows the true yearly yield (APY/AER) for the chosen compounding frequency.
Stacked growth chart
Each bar splits the balance into what you paid in and what interest added — hover for exact values.
Years and months
Handles periods like 7 years 6 months without rounding to whole years.
The compound interest formula
For a single deposit the future value is A = P × (1 + r/n)n·t, where P is the principal, r the annual rate as a decimal, n the number of compounding periods per year and t the time in years. With continuous compounding it becomes A = P × er·t. The interest earned is A − P.
Regular contributions are added as a series of deposits. For a deposit C made at the end of every compounding period the future value is C × ((1 + i)N − 1) ÷ i, with i = r/n and N = n·t; deposits at the start of each period are multiplied by a further (1 + i). When the deposit frequency differs from the compounding frequency, the calculator uses the equivalent monthly growth factor (1 + r/n)n/12, so each deposit earns exactly the compounding it would receive.
Example: $10,000 at 8% compounded monthly for 10 years grows to $22,196.40. Add $100 at the end of every month and the balance reaches $40,491.01: $22,000 of contributions and $18,491.01 of interest.
How compounding frequency changes the result
$10,000 at a nominal 8% for 10 years. More frequent compounding helps, but the gains shrink quickly after monthly:
| Compounding | Final balance | Effective annual rate |
|---|---|---|
| Yearly | $21,589.25 | 8.000% |
| Half-yearly | $21,911.23 | 8.160% |
| Quarterly | $22,080.40 | 8.243% |
| Monthly | $22,196.40 | 8.300% |
| Daily | $22,253.46 | 8.328% |
| Continuous | $22,255.41 | 8.329% |
Tips to make compounding work for you
- Start early. Time matters more than rate: by the rule of 72, money at 8% doubles roughly every 9 years (72 ÷ 8).
- Compare effective rates, not headline rates. A 7.9% rate compounded monthly beats 8% compounded yearly.
- Keep contributing. Small regular deposits often end up larger than the starting amount — see how a monthly plan grows with the SIP calculator.
- Mind inflation and tax. A 6% return with 5% inflation is only about 1% of real growth; check it with the inflation calculator.
- For a quick comparison with interest that does not compound, use the simple interest calculator.
Compound Interest Calculator FAQ
How do I calculate compound interest?
Use A = P × (1 + r/n)^(n·t). Divide the annual rate by the number of compounding periods, add 1, raise it to the total number of periods and multiply by the principal. This compound interest calculator does it for you and adds regular contributions.
What is the difference between simple and compound interest?
Simple interest is paid only on the original principal. Compound interest is also paid on interest already earned, so the balance grows faster the longer you leave it.
What is the effective annual rate (EAR or APY)?
It is the actual yearly growth after compounding: (1 + r/n)^n − 1. For example, 12% compounded monthly gives an effective annual rate of 12.683%.
Does daily compounding make a big difference?
Only a small one. At 8%, daily compounding gives an effective rate of 8.328% versus 8.300% for monthly. The rate itself and the time you stay invested matter far more.
Should contributions be at the start or end of the period?
Choose what matches reality. Money deposited at the start of each month earns one extra month of interest every time, so the final balance is a little higher.
Are the results guaranteed?
No. Fixed-rate deposits will be close, but market investments go up and down and taxes and fees reduce returns. Use the figures as estimates for planning, not financial advice.