Compound Interest Calculator
Free compound interest calculator with daily, monthly, and annual compounding. See final balance, total interest earned, growth with monthly contributions, and a full year-by-year table.
Example Scenarios
Savings Growth
$10k • 5% • 10 yr
Long Term
$10k • 7% • 20 yr
Monthly Deposits
$200/mo • 7% • 30 yr
Principal + Deposits
$5k + $100/mo • 6%
Growth Details View Results
Compound Growth Results
Growth Over Time
Compounding Frequency Comparison
| Frequency | Final Balance | Interest |
|---|
Year-by-Year Growth
| Year | Start | Contributions | Interest | End |
|---|
How This Is Calculated
Compound interest uses A = P(1 + r/n)nt for the starting principal, plus month-by-month compounding for any deposits. Your numbers are plugged in below:
Everything behind the Compound Interest Calculator
Formulas, reference charts, and detailed answers — expand any section you need.
Daily vs Monthly vs Annual Compounding
More frequent compounding earns more at the same stated rate, but the gap is smaller than most people expect, and it shrinks as a share of the balance over time. The frequency comparison table runs your exact inputs at all four frequencies so the real difference is visible.
| Compounding | $10,000 at 5% for 10 Years |
|---|---|
| Annually | $16,289 |
| Quarterly | $16,436 |
| Monthly | $16,470 |
| Daily | $16,487 |
The lesson: rate and time dominate; frequency fine-tunes.
How Long Does It Take Money to Double? The Rule of 72
Divide 72 by your annual rate to estimate the years needed to double: at 6%, about 12 years; at 9%, about 8 years. It's an approximation of the compound formula that works well for rates between 4% and 12%, and it's the fastest way to sanity-check any growth projection without a calculator.
| Annual Rate | Years to Double (Rule of 72) |
|---|---|
| 4% | 18 years |
| 6% | 12 years |
| 8% | 9 years |
| 10% | 7.2 years |
Compound Interest Calculator: How Your Money Grows
This compound interest calculator shows what happens when interest earns interest. Enter a starting amount, annual rate, time period, and compounding frequency, and the calculator displays the final balance, total interest, and a year-by-year growth table instantly. Add monthly contributions to model real saving behavior, and the growth chart splits the final balance into principal, deposits, and interest so you can see exactly what compounding contributed.
Example: $10,000 at 7% compounded monthly for 20 years grows to $40,387, with $30,387 of it interest.
The Compound Interest Formula Explained
Compound interest uses A = P(1 + r/n)^(nt), where P is the starting principal, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is time in years. The exponent is what separates compounding from simple interest: each period's interest joins the balance and earns its own interest in every period after. The calculator applies the formula automatically and shows it with your numbers in the trust section.
Worked example: $5,000 at 6% compounded monthly for 10 years: A = 5000(1 + 0.06/12)^(120) = $9,097.
Compound Interest Calculator With Monthly Contributions
Regular deposits transform the math, because every contribution starts its own compounding clock. A modest monthly deposit sustained over decades routinely out-earns a much larger lump sum added late. The contributions layer in the chart makes this visible: early money has time to compound, late money doesn't.
Example: $200 per month at 7% for 30 years, with no starting balance, grows to about $243,000, of which roughly $171,000 is interest.
Compound Interest vs Simple Interest
Simple interest pays only on the principal; compound interest pays on the principal plus everything already earned. Over short periods the difference is minor. Over decades it's the majority of the balance: $10,000 at 7% for 30 years earns $21,000 simple but $71,165 compounded monthly. The calculator shows the compounding bonus as its own line so the gap is never abstract.