Financial Calculator

Compound Interest Calculator

See how your money grows with daily, monthly, or annual compounding — complete with a year-by-year growth chart.

Investment Details
$
$10,000
$
$200/mo
What you add every month. Each deposit goes in at the end of the month.
%
7.0%
years
20 yrs
This is called compounding. Most savings accounts add interest daily or monthly.
Results
Future value
Total you put in
Interest earned
Total gain
Interest as a share of what you put in
Effective yearly rate (APY)
Your rate after compounding
Year-by-Year Breakdown
Year Start balance Contributions Interest End balance

What Is Compound Interest?

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest (which only grows on the original principal), compound interest causes your money to grow exponentially — your interest earns interest.

The Compound Interest Formula

A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)]

Where A = final amount, P = principal, r = annual rate, n = compounding periods/year, t = years, PMT = contribution per period. The formula above is exact when deposits and compounding are both monthly (n = 12). For daily, quarterly, or annual compounding, this calculator converts the rate to its monthly equivalent and adds your deposit at the end of each month.

The Rule of 72: Divide 72 by your annual return to estimate years to double. At 7%, money doubles in ~10.3 years. At 10%, in ~7.2 years. This is a quick mental math shortcut used by investors worldwide.

Daily vs. Monthly vs. Annual Compounding

The more frequently interest compounds, the more you earn — but the difference between daily and monthly compounding is surprisingly small. On a $10,000 investment at 5% for 10 years: daily compounding yields $16,487, monthly yields $16,470, and annual yields $16,289. The time you stay invested matters far more than compounding frequency.

Why Regular Contributions Matter More Than the Starting Amount

A person who invests $200/month starting at age 25 will typically accumulate more wealth than someone who invests $500/month starting at 40, even though the late starter contributes more money total. This is the power of time in compound interest — starting early is worth more than starting bigger.