Enter your initial principal, annual interest rate, how many years you plan to invest, the compounding frequency, and an optional monthly contribution. The calculator instantly shows your final balance and a year-by-year breakdown.
The compounding frequency matters: money compounded monthly grows faster than money compounded annually at the same rate, because interest starts earning interest sooner.
Where P = principal, r = annual rate (decimal), n = compounding periods per year, t = years, PMT = contribution per compounding period.
Example: €10,000 at 7% for 20 years
Scenario
Monthly contrib
Final balance
Total interest
Lump sum only
€0
~€38,700
~€28,700
+ €200/month
€200
~€104,000
~€56,000
+ €500/month
€500
~€216,000
~€96,000
Adding regular contributions makes a dramatic difference over long periods.
Compounding frequency: does it matter?
Yes, but less than most people think. The difference between monthly and daily compounding at 7% over 20 years on €10,000 is roughly €150. The rate and the time horizon matter far more.
Rule of 72
A quick mental shortcut: divide 72 by the annual rate to estimate how many years it takes to double your money. At 7%, your money doubles roughly every 72 ÷ 7 ≈ 10 years.
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