Compound Interest Calculator
Project how money grows when interest earns interest. Start with a lump sum, add regular deposits, and see the final balance split into what you put in and what it earned.
- Runs in your browser
- No sign-up
- Free to use
Growth by year
- Contributions
- Interest
Year-by-year table
| Year | Contributed | Interest earned | Balance |
|---|
How to use Compound Interest Calculator
- Enter your starting amount and how much you will add each month.
- Enter the expected annual interest rate and the number of years.
- Choose how often interest is compounded: yearly, quarterly, monthly or daily.
- Read the future value and see the year-by-year chart of contributions versus interest.
Compound Interest Calculator features
Regular contributions
Model monthly deposits on top of an initial amount.
Five compounding frequencies
Annual, semi-annual, quarterly, monthly and daily.
Contributions versus growth
The result separates the money you paid in from the interest earned.
Year-by-year chart and table
Watch the interest portion overtake your contributions over time.
Effective annual rate
Shows the true yearly yield once compounding is taken into account.
Any currency
Results are formatted in the currency you select.
When to use Compound Interest Calculator
- Estimating how much a savings plan could be worth at retirement.
- Seeing the effect of starting to invest five years earlier or later.
- Comparing accounts with different rates and compounding periods.
- Setting a monthly saving amount to reach a target sum.
Compound Interest Calculator FAQ
What is compound interest?
Interest calculated on the original amount plus all the interest already added. Because each period's interest increases the balance, growth accelerates over time, unlike simple interest, which is earned on the original amount only.
What is the compound interest formula?
A = P × (1 + r ÷ n)^(n × t), where P is the starting amount, r the annual rate as a decimal, n the number of compounding periods per year and t the number of years. Regular contributions are added period by period.
Does compounding frequency make a big difference?
A modest one. At 6% a year, 10,000 becomes 17,908 after ten years with annual compounding and 18,194 with monthly compounding. The rate and the time invested matter far more.
Are the results guaranteed?
No. The calculator assumes a constant rate and no taxes, fees or inflation. Savings account rates change and investment returns vary from year to year, so treat the result as an illustration.
When are contributions assumed to be made?
At the end of each month. Depositing at the start of the month instead would give a slightly higher result.
Why time matters more than rate
Compounding is exponential: the balance grows by a percentage of itself, so the amount added each year keeps increasing. In the first years the effect is barely visible, because the interest is small compared with what you contribute. Later the interest earned each year can exceed your yearly deposits, and the curve bends sharply upwards.
This is why starting early matters so much. Someone who saves for forty years typically ends up with far more than twice the balance of someone who saves the same monthly amount for twenty, because the early contributions have had decades to grow. A useful shortcut is the rule of 72: divide 72 by the annual rate to estimate the years needed for money to double. At 6% that is about twelve years.
Real returns are lower than headline rates once inflation, tax and charges are taken into account. For long-term planning it is sensible to enter a rate net of expected inflation, so the result is expressed in today's money.