TimeValue

Compound Interest Calculator

Plug in a principal, rate, and time frame — see exactly how compounding frequency changes your final balance.

Starting principal

Annual interest rate

Time period (years)

Compounding frequency

Balance after 10 years

$18,194

$8,194 in interest earned

Starting principal: $10,000
Total interest earned: $8,194

What you entered

Principal: $10,000Annual rate: 6%Compounding: MonthlyYears: 10

1
Convert the annual rate to a per-period rate (compounding monthly)
6% ÷ 12= 0.5000%
2
Total number of compounding periods
12 × 10 years= 120 periods
3
Apply the compound interest formula
A = P × (1 + r/n)ⁿᵗ = $10,000.00 × (1 + 0.0050)^120= $18,193.97
4
Interest earned
$18,193.97 − $10,000.00 principal= $8,193.97

Result

Balance after 10 years: $18,194

$10,000 compounding monthly at 6% grows to $18,194 in 10 years — $8,194 of that is interest, not your own money.

What $10,000 grows to at common return rates

Every figure is a $10,000 lump sum compounded monthly at the rate in the column heading, with no further deposits, run through the same formula this calculator uses: A = P x (1 + r/n)^nt.

Time invested	At 4%	At 6%	At 8%	At 10%
1 year	$10,407	$10,617	$10,830	$11,047
3 years	$11,273	$11,967	$12,702	$13,482
5 years	$12,210	$13,489	$14,898	$16,453
10 years	$14,908	$18,194	$22,196	$27,070
15 years	$18,203	$24,541	$33,069	$44,539
20 years	$22,226	$33,102	$49,268	$73,281
25 years	$27,138	$44,650	$73,402	$120,569
30 years	$33,135	$60,226	$109,357	$198,374

Read down a column rather than across a row: at 8% the money takes about 9 years to double the first time but adds nearly $36,000 between year 25 and year 30 alone, because each year compounds on a larger base. Nothing here is adjusted for inflation, tax or fees, all three of which are real. A 1% annual fee on the 8% column would cost about $28,000 over 30 years. These are illustrative rates, not a forecast - actual returns arrive unevenly, and a sequence of poor early years produces a very different result from the same average.

Why compounding frequency matters

The same rate compounded daily earns slightly more than compounded annually, because interest starts earning its own interest sooner. The difference grows with higher rates and longer time frames.

Compound vs. simple interest

Simple interest only ever applies to the original principal. Compound interest applies to principal plus all previously earned interest — over long periods this gap becomes enormous.

Frequently asked questions

What is the compound interest formula?

A = P(1 + r/n)^(nt), where P = principal, r = annual rate (as decimal), n = compounding frequency per year, t = years. For $10,000 at 5% compounded monthly for 10 years: A = 10,000 × (1 + 0.05/12)^(12×10) = $16,470.09.

How does compounding frequency affect returns?

$10,000 at 5% for 10 years: compounded annually = $16,288.95, monthly = $16,470.09, daily = $16,486.65. The difference between annual and daily compounding is about $198 — meaningful but not dramatic at typical savings rates.

What is the Rule of 72?

Divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 6%, money doubles in about 12 years. At 8%, about 9 years. It's a quick mental shortcut that's accurate for rates between 2–15%.