Compound Interest Calculator
Calculate compound interest with monthly contributions. See growth projections, total interest earned, and year-by-year breakdown. No signup required.
Investment Parameters
Results
Final Amount
$54,713.58
Principal
$10,000.00
Total Interest
$20,713.58
Total Contributions
$24,000.00
Growth Over Time
How to Use Compound Interest Calculator
- 1
Enter principal
Enter your initial investment amount.
- 2
Set rate and time
Enter the annual interest rate and number of years.
- 3
Choose frequency
Select how often interest compounds: daily, monthly, quarterly, or yearly.
- 4
Add contributions
Enter any recurring monthly contribution amount.
- 5
View results
See your final amount, total interest, and year-by-year growth chart.
Frequently Asked Questions
Related Tools
How Compound Interest Actually Works
There's a quote often attributed to Einstein calling compound interest the eighth wonder of the world. Whether he actually said it is debatable, but the math behind it is genuinely remarkable. Compound interest means you earn interest on your interest — your balance grows, and next period's interest is calculated on that larger balance. The effect starts subtle and becomes dramatic over time.
Here's a concrete example. Put $10,000 in an account earning 7% annually. After year one you have $10,700. After year two, you earn 7% on $10,700 — not on the original $10,000 — giving you $11,449. By year 10, you have $19,672. By year 20, $38,697. By year 30, $76,123. The original $10,000 grew more than 7x over 30 years with no additional contributions, just time and compounding.
The Rule of 72
The Rule of 72 is a mental shortcut for estimating how long it takes to double your money. Divide 72 by your annual interest rate, and you get the approximate number of years to double. At 6%, you double in 12 years. At 8%, about 9 years. At 12%, about 6 years. It's not exact, but it's close enough for quick comparisons and surprisingly accurate across the 4-15% range.
Why Starting Early Matters More Than Investing More
This is the lesson most financial educators hammer on, and the numbers actually back it up. Consider two people: Sara starts investing $200/month at age 25 and stops at 35 — only 10 years of contributions, $24,000 total. Mike starts at 35 and invests $400/month (twice as much) until 65 — 30 years of contributions, $144,000 total. Assuming 7% annual returns, Sara ends up with more money at 65 despite investing far less, simply because her money had an extra decade to compound.
The implication: the single best financial decision you can make in your 20s isn't choosing the right stocks — it's starting. Even small amounts invested early beat larger amounts invested later.
Compounding Frequency: Does It Matter?
Banks and investment products often advertise daily, monthly, or quarterly compounding as a selling point. In reality, the difference between compounding frequencies matters less than most people expect. $10,000 at 7% for 30 years: annual compounding gives you $76,123. Monthly compounding gives you $81,165. Daily compounding gives $81,635. The gap between monthly and daily is only $470 over 30 years — negligible. The rate and the time horizon matter far more than how often interest compounds.