Compound Interest Calculator

See how principal and regular contributions grow over time.

Set your starting balance, annual rate, compounding frequency, and optional monthly deposits. The schedule shows balance and interest earned each year.

Growth Inputs

Year-by-Year Balance

YearBalanceInterest earnedContributions

Practical tips & common mistakes

Start early, even small

Compound growth is dominated by time in market. Ten extra years often beats doubling your contribution rate.

Ignoring contribution timing

Monthly deposits at period-end vs period-start change results. Match how your brokerage actually debits your account.

Nominal vs real return

Subtract expected inflation from your rate when planning retirement purchasing power — 7% nominal might be 4% real.

Rule of 72

Divide 72 by your annual % return for a rough doubling time. At 8%, money doubles in about 9 years.