Compound Interest Calculator
What your savings grow to with compound interest and monthly deposits, what to save for a goal, and what waiting costs.
What do you want to know?
More optionsMonthly deposits, monthly compounding
Deposits
Made at the end of each month or year.
Interest is added
Barely moves the result; most savings accounts compound daily or monthly.
In 20 years
$300,851
$171k of it is interest.
- Interest passes deposits
- Year 17
- Money doubles about every
- 10.3 years
- Interest in the final year
- $20,061
Year-by-year breakdownBalance, deposits and interest
How it’s worked outA = P(1 + r/n)^(nt), plus each deposit grown from its own date
The starting amount grows by (1 + 7% ÷ 12)12 × years. Each deposit is made at the end of its month and compounds from then on, so the deposits form a geometric series.
Estimates only. Real returns vary year to year and aren’t guaranteed; fees and taxes aren’t included.
Frequently Asked Questions
What is the difference between compound and simple interest?
Simple interest is calculated only on the original principal amount. Compound interest is calculated on the principal plus any previously earned interest, so your money grows exponentially. For example, $1,000 at 5% simple interest earns $50/year forever, while compound interest earns more each year because interest earns interest.
How does compounding frequency affect returns?
More frequent compounding produces slightly higher returns because interest is calculated and added to the principal more often. For example, $10,000 at 5% for 10 years yields $16,288.95 with annual compounding, $16,470.09 with monthly, and $16,486.65 with daily compounding. The difference grows with higher rates and longer time periods.
What is the Rule of 72?
The Rule of 72 is a quick way to estimate how long it takes to double your money. Divide 72 by your annual interest rate to get the approximate number of years. For example, at 6% interest, your money doubles in roughly 72/6 = 12 years. It works best for rates between 4% and 12%.
How can I maximize my compound interest returns?
Start investing as early as possible to give compounding more time to work. Choose investments with higher interest rates when appropriate for your risk tolerance. Select accounts with more frequent compounding (monthly or daily over annually). Reinvest all earnings rather than withdrawing them, and make regular additional contributions.
What is the compound interest formula?
The formula is A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate as a decimal, n is the number of compounding periods per year, and t is the number of years. With recurring contributions, each deposit also compounds for the remaining time, which this calculator handles by growing every deposit from the date it is made, at your chosen compounding frequency.
How much do I need to invest each month to reach a goal?
Choose "Reach a goal", enter the target and the number of years, and the calculator solves for the monthly amount: the goal minus what your starting balance grows to, divided by what each $1 a month grows to by then. Tick "In today's dollars" to treat the goal as today's money, so it is raised by inflation first.
What does waiting to invest cost?
Choose "Cost of waiting" to compare starting now with starting the same plan a few years later, ending at the same date. Because the earliest deposits compound the longest, a five-year delay often costs far more than the five years of contributions you skipped.