Compound interest is often called the most powerful force in personal finance ā not because the math is complicated, but because the effect is easy to underestimate over long time horizons.
Simple vs. compound interest
Simple interest is calculated only on your original principal. Compound interest is calculated on your principal plus any interest already earned ā meaning your money starts earning on its own earnings.
- Annual compounding adds interest once a year.
- Monthly compounding adds interest 12 times a year, growing slightly faster.
- Daily compounding grows fastest, common in high-yield savings accounts.
Example: $10,000 at 6% annual interest becomes about $18,000 after 10 years, but nearly $32,000 after 20 ā the growth curve steepens the longer you leave it invested.
The takeaway
The single biggest lever in compound growth isn't the rate ā it's time. Starting a few years earlier, even with smaller contributions, usually beats starting later with larger ones.
PrimeCalculator Editorial Team
Calculator & Finance Writers