Albert Einstein allegedly called compound interest "the eighth wonder of the world." Whether or not he actually said it, the sentiment is absolutely correct. Compound interest is what makes your money grow over time — and understanding it is essential for building wealth.
💡 Quick Formula: A = P(1 + r/n)^(nt)
Where A = final amount, P = principal, r = annual rate, n = compounding frequency, t = time in years
The Compound Interest Formula
The basic formula for compound interest is:
A = P(1 + r/n)^(nt)
What Each Variable Means:
- A = The final amount (principal + interest)
- P = Principal (your initial investment)
- r = Annual interest rate (as a decimal)
- n = Number of times interest compounds per year
- t = Time in years
Real Example
Let's say you invest $10,000 at 7% annual interest compounded annually for 10 years:
A = 10000(1 + 0.07/1)^(1×10)
A = 10000(1.07)^10
A = 10000 × 1.967
A = $19,671.51
Your $10,000 nearly doubled in 10 years — that's the power of compound interest!
Try It Yourself
Don't want to do the math manually? Use our free compound interest calculator:
📊 Open Compound Interest Calculator →Compound Interest vs Simple Interest
With simple interest, you only earn interest on your principal. With compound interest, you earn interest on your interest:
| Year | Simple Interest (5%) | Compound Interest (5%) |
|---|---|---|
| 1 | $500 | $500 |
| 5 | $2,500 | $2,762 |
| 10 | $5,000 | $6,289 |
| 20 | $10,000 | $15,330 |
How Often Does Interest Compound?
- Annually = once per year (n=1)
- Quarterly = 4 times per year (n=4)
- Monthly = 12 times per year (n=12)
- Daily = 365 times per year (n=365)
The more frequently interest compounds, the more you earn. But for most savings accounts and investments, the difference between monthly and daily compounding is minimal.
Key Takeaways
- ✅ Compound interest earns interest on interest
- ✅ Time is your biggest ally — start early!
- ✅ Higher frequency = slightly more earnings
- ✅ Even small amounts grow significantly over time
Start Calculating Today
Use our free compound interest calculator to see how your money can grow:
Try Compound Interest Calculator →Last updated: March 2026