Finance & Money
Compound Interest Calculator
Project how money grows with compound interest, monthly contributions, and inflation, or work backward from a target savings goal to the monthly contribution you need.
Future value
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- Total contributed
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- Interest earned
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- Today's dollars
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Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
Use this calculator with
Follow these when you want the formula behind the answer, a short lesson, or nearby tools in the same topic.
What this compound interest calculator can solve
| Mode | Use it when | Output |
|---|---|---|
| Future value | You know starting amount, contribution, rate, and time | Future value, interest earned, and inflation-adjusted value |
| Monthly contribution for target | You have a savings goal | Required monthly contribution and future value breakdown |
Compound interest formula
P is starting principal, r is annual return, n is compounding periods per year, t is years, and PMT is the contribution per compounding period.
Why inflation matters
Nominal future value tells you the dollar balance. Inflation-adjusted value estimates purchasing power in today's dollars.
Rule of 72
A quick estimate for doubling time is 72 divided by the annual return percentage. At 7%, money doubles in about 10.3 years.
Worked examples
$1k seed + $100/mo for 20 years at 7%
Future value with monthly contributions
Future value
$56,131.40
$100k target in 20 years
Required monthly contribution
Future value
$100,000.00
$10k one-time for 30 years at 8%
Long-term compounding
Future value
$109,357.30
Frequently asked questions
Are monthly contributions compounded monthly?+
The calculator converts monthly contributions into the selected compounding period. For monthly compounding, contributions are monthly.
Does this include taxes?+
No. Taxable accounts can lose some growth to taxes. Tax-advantaged accounts like Roth IRA, traditional IRA, or 401(k) accounts have different tax treatment.
Is 7% a guaranteed return?+
No. It is a common long-term planning assumption, not a guarantee. Real investments fluctuate and can lose value.
Why show inflation-adjusted value?+
Because future dollars may buy less than today's dollars. Inflation-adjusted value gives a rough purchasing-power estimate.
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Last updated: May 8, 2026