Compound Interest Calculator
See how a starting balance plus regular monthly contributions grow with compound interest over time.
Reviewed October 7, 2026 Runs in your browser — inputs are never stored
Future balance
$124,379.03
- Total contributed
- $53,000.00
- Interest earned
- $71,379.03
Balance growth vs. contributions
Where your balance comes from
$124.4K
Future balance
This tool provides general financial estimates for educational purposes only and is not personalized financial, tax, or investment advice. Consult a licensed financial professional before making major financial decisions.
About the Compound Interest Calculator
A compound interest calculator is a long-term savings tool that shows how a starting balance plus regular contributions grow over time when earnings are reinvested. It is built for savers planning retirement, parents building education funds, investors comparing scenarios, and anyone who wants to see the real power of compounding. Enter your initial deposit, monthly contribution, expected annual return, and time horizon, and the calculator projects the future value using the standard compound-interest formula, with monthly compounding and contributions. The result makes two things visible at once: how much of your final balance comes from your own contributions versus from growth, and how starting earlier dramatically outweighs saving more later. By turning abstract percentages into concrete future values, the tool helps you set realistic goals and stay motivated. All calculations run locally in your browser, keeping your figures private. Remember that real returns vary with markets and inflation; for personalised financial planning, consult a qualified adviser.
How to use it
- 1Enter your starting principal (initial balance).
- 2Set the annual interest rate and how often it compounds.
- 3Add regular contributions if you save monthly or yearly.
- 4Choose the investment horizon in years.
- 5Calculate to see future value, interest earned, and growth path.
Worked example
$10,000 starting balance, 7% annual return, monthly compounding, $200 added each month for 20 years. The future value is about $144,600, with most of the gain coming from compounded growth on both the seed capital and contributions. Compare “contributions only” versus “with growth” to see the power of time in the market.
How it works
How it works
Your initial deposit compounds monthly, and each monthly contribution earns interest from the moment it is added.
Formula
FV = P(1+i)ⁿ + PMT × [((1+i)ⁿ − 1) / i]
Who it is for
Savers planning retirement, parents building education funds, investors comparing scenarios, and anyone who wants to see how a starting balance plus regular monthly contributions grow when earnings are reinvested.
Why it helps
Compounding turns small, steady contributions into large future balances, but the effect is invisible without a projection — the tool shows how much of your final balance is growth versus contributions.
Tips for better results
- Reduce the return rate by ~2–3% to approximate real (inflation-adjusted) growth, since the default shows nominal values.
- Compare starting at age 25 vs 35 with the same monthly contribution — the decade difference often outweighs saving twice as much later.
- Enter contributions as monthly, since the model compounds monthly; an annual lump sum needs dividing by 12 for an accurate comparison.
- Stress-test with a lower return (e.g. 5% instead of 8%) to see a conservative downside scenario.
Common mistakes to avoid
- Entering an annual return where the monthly rate is implied — the calculator divides by 12 internally, so use the annual figure.
- Forgetting that real returns are lower than nominal returns once inflation is accounted for.
- Assuming past market returns (7–10%) are guaranteed for the future.
- Ignoring taxes and fees, which can cut net returns by 1–2% per year.
Frequently asked questions
A:Yes — starting earlier gives compounding more time to work, often outweighing larger later contributions.
A:Yes, contributions and compounding both occur monthly in this model.
A:No, results are nominal. Reduce the return rate to approximate real (inflation-adjusted) growth.
Reviewed for accuracy · Last updated October 7, 2026
Formulas follow standard amortization, present/future value, and compounding mathematics used throughout the financial industry, and are periodically checked against reference calculations.
CalcWisee Editorial Team
Calculator development and formula review
CalcWisee is an independent site founded by Ayman. Every calculator is built from a published formula or official definition, tested against hand-worked examples before it goes live, and corrected promptly when a reader reports an issue to ayman@calcwisee.com.
Expertise: Financial mathematics, Health and fitness formulas, Applied mathematics, Unit conversion standards
References & sources
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