Calculators
Compound Interest Calculator
See how an investment grows over time. Choose your rate, compounding frequency, and optional monthly contributions, then watch the balance pull away from your contributions.
| Year | Balance | Contributions | Interest |
|---|---|---|---|
| 0 | €1,000.00 | €1,000.00 | €0.00 |
| 1 | €1,070.00 | €1,000.00 | €70.00 |
| 2 | €1,144.90 | €1,000.00 | €144.90 |
| 3 | €1,225.04 | €1,000.00 | €225.04 |
| 4 | €1,310.80 | €1,000.00 | €310.80 |
| 5 | €1,402.55 | €1,000.00 | €402.55 |
| 6 | €1,500.73 | €1,000.00 | €500.73 |
| 7 | €1,605.78 | €1,000.00 | €605.78 |
| 8 | €1,718.19 | €1,000.00 | €718.19 |
| 9 | €1,838.46 | €1,000.00 | €838.46 |
| 10 | €1,967.15 | €1,000.00 | €967.15 |
How compound interest works
Compound interest is interest earned on both your original money and the interest it has already earned. Each period the balance grows, and the next period's interest is worked out on that larger balance, so growth speeds up the longer you stay invested.
A = P(1 + r/n)nt + PMT × (((1 + r/n)nt - 1) / (r/n))- A final balance
- P starting amount
- r annual rate
- n times compounded per year
- t years
- PMT periodic contribution
Compounding frequency is how often interest is added to the balance. More frequent compounding gives a slightly higher result for the same rate. Regular contributions add to the balance and then earn their own compound interest, which is what builds wealth over many years.
Example growth
Final balance for a €10,000 starting amount with no extra contributions, compounded annually. Longer time horizons and higher rates show the effect most clearly.
| Annual rate | 10 years | 20 years | 30 years |
|---|---|---|---|
| 4% | €14,802 | €21,911 | €32,434 |
| 6% | €17,908 | €32,071 | €57,435 |
| 8% | €21,589 | €46,610 | €100,627 |
Frequently asked questions
What is compound interest?
Compound interest is interest earned on both your original money and the interest it has already earned. Because each period's interest is added to the balance, future interest is calculated on a larger amount, so the balance grows faster the longer it is left.
How does compounding frequency affect my returns?
More frequent compounding, such as daily or monthly rather than annually, adds interest to the balance sooner, so it earns slightly more for the same nominal rate. The difference is small at low rates and grows at higher rates and over longer periods.
Do regular contributions really make a difference?
Yes, and the effect is large over time. Each contribution earns its own compound interest for the rest of the term, so steady monthly investing usually ends well ahead of a single lump sum left untouched.
What annual return should I assume?
It depends on where the money sits. Savings accounts are typically low single digits, while long-term diversified stock market averages have historically been higher but vary year to year and are never guaranteed.
Does this calculator account for inflation or tax?
No, it shows nominal growth before inflation and tax. Your real spending power will be lower over time, and any tax on the interest or gains depends on your country and the type of account.