Skip to content

Compound Interest Calculator

Compound interest is why saving pays off so much over the long run: you earn interest not just on your deposit, but on the interest from previous years too. This calculator shows what your savings are worth after a chosen period, including an optional fixed monthly deposit.

ยฃ
ยฃ
%
years

Result

ยฃ31,998.32

Final value

Total deposited
ยฃ22,000.00
Total interest
ยฃ9,998.32
How this was calculated
  1. 1Find the monthly rate5% รท 12 = 0.4167%
  2. 2Calculate the growth factor over the term(1 + 0.004167)^120 = 1.647
  3. 3Starting amount times growth factor, plus the deposits with interest

Formula

FV = P ร— (1 + i)โฟ + PMT ร— (((1 + i)โฟ โˆ’ 1) รท i)

The first part calculates what your starting amount alone becomes. The second part adds up the growth of each monthly deposit separately, because a deposit in year 1 has longer to grow than one in year 9.

What the variables mean

P
Starting amount โ€” โ‚ฌ
PMT
Monthly deposit โ€” โ‚ฌ
i
Monthly rate (annual rate รท 12 รท 100)
n
Number of months

Worked examples

โ‚ฌ 10,000 starting amount, no deposits, 5% rate, 20 years

โ†’ Final value โ‰ˆ โ‚ฌ 26,533.

โ‚ฌ 0 starting amount, โ‚ฌ 200/month, 4% rate, 30 years

โ†’ Final value โ‰ˆ โ‚ฌ 138,600, of which โ‚ฌ 66,600 is interest.

Common mistakes

  • Using the annual rate as the monthly rate. Always divide by 12 first.
  • Forgetting inflation erodes the purchasing power of the final amount; use a real (post-inflation) rate if relevant.

Tips

  • Starting early outweighs depositing more later โ€” time is the most powerful factor in compound interest.

Important to know

  • This is an indicative calculation with a fixed rate. Real savings and investment returns fluctuate year to year.

When to use it

  • Estimating what a savings account yields over 10 or 20 years.
  • Visualising the effect of starting to save earlier.

Frequently asked questions

What is the difference between simple and compound interest?

With simple interest you earn interest on the same starting amount every year. With compound interest you also earn interest on the interest already accrued, which accelerates growth.

How often is interest credited here?

This calculator assumes monthly crediting, the most common frequency for Dutch savings accounts.

In summary

The longer your money has to grow, the larger the share of compound interest in the final result. Use this calculator to compare different terms and deposit amounts before setting a savings or investment goal.

Was this calculator helpful?