Compound Interest Calculator
See how savings grow with compound interest. Enter an initial amount, monthly contribution, rate and term to get the final value, total gain and a yearly table.
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Key Formula & Conditions
Learning modelComputes compound balance A = P(1 + r/n)^(nt) on annual/monthly intervals. Models regular monthly contributions, compares compound growth against simple interest, and calculates doubling time using the Rule of 72 (years ≈ 72 / interest rate %).
Final value
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Total invested
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Total gain
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Term (months)
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Yearly breakdown
| Year | Contributed in year | Gain in year | Value at year end |
|---|
A monthly-compounded estimate. Taxes and fees are ignored and market risk is not reflected. Results are not guaranteed — this is not investment advice.
Done
Compound Interest Calculator
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Worked Examples & Verified Values
1M yen at 5% for 10y
30k/mo savings at 4% for 20y
Rule of 72 doubling time
Common Pitfalls & Calculation Rules
- •Confusing simple and compound interest. Compounding adds earned interest back into principal, creating exponential growth over long horizons.
- •Overlooking compounding frequency. Monthly compounding produces a higher effective annual yield (APY) than annual compounding at the same nominal rate (APR).
- •Ignoring inflation and investment taxes (e.g. ~20.315% capital gains withholding in Japan). Real returns after taxes and inflation reflect purchasing power.
Verification scope and citation information
Use worked examples within their stated inputs, units and assumptions. Tests cover specific cases at a specific time; they do not certify every input, expert review or standards compliance. Check the references and tool-specific verification notes, and enter your own access date when citing.
@misc{tools_hub_compound_interest_calculator_2026,
author = {{Tools Hub}},
title = {Compound Interest Calculator},
year = {2026},
url = {https://the-tools-hub.net/en/tools/compound-interest-calculator/},
note = {Accessed: YYYY-MM-DD}
}How to use
- 1
Enter amounts
Fill in the initial amount and the monthly contribution (either one alone works too).
- 2
Set rate and term
Choose an annual rate and the term (years plus extra months).
- 3
Review the growth
Check the final value, total gain and the year-by-year table of principal and value.
Features
- Compound simulation for an initial amount plus monthly contributions
- Instant final value, total invested and total gain
- Year-by-year table of contributions, gains and value
- Everything computed in your browser; nothing is transmitted
Use cases
Projecting recurring investments
Estimate the value of monthly contributions at an assumed rate in 10 or 20 years.
Saving for a down payment
Work out how term and monthly amount combine toward a target.
Education savings
Compare contribution plans against a school-enrollment deadline.
Details
Compound interest means earned gains are added back to the balance and keep earning. Both the initial amount and each monthly contribution grow at the monthly rate: the initial amount scales by (1 + r)^n, and the contributions grow by ((1 + r)^n − 1) ÷ r, where r is the monthly rate and n the number of months. Their sum is the final value.
This tool approximates monthly compounding by dividing the annual rate by 12 and rounds displayed amounts to whole currency units. Real investing involves taxes, fees, price fluctuations and rate changes, so use these numbers to understand the mechanics and sketch a plan — not as a promise of results. Nothing here is principal-guaranteed or investment advice.
Typical uses: estimating where recurring savings could end up, working backwards from a target to a monthly contribution, and seeing how strongly rate and duration affect the outcome. The yearly table shows the moment gains start exceeding contributions — the essence of compounding.
Compound Interest, Loans & Margins
Simulate long-term compound growth with Rule of 72, amortized loan repayments, and tax/profit margin metrics.
FAQ
What is compound interest?
It is the mechanism where earned gains are added back to the balance and start earning on their own. Compared to simple interest, growth accelerates the longer the term runs.
Does the result match real investment performance?
No. This is a monthly-compounded estimate that ignores taxes, fees, price fluctuations and rate changes. Real results vary with the market.
Can I calculate with a zero initial amount?
Yes. Either the initial amount or the monthly contribution alone is enough — only both being zero is an error.
Are the amounts I enter sent anywhere?
No. All computation happens locally in your browser and nothing you enter is transmitted.
What is the Rule of 72?
A mental arithmetic rule to estimate the years needed to double an investment: Years ≈ 72 / Interest Rate (%). Derived from natural logarithm ln(2) ≈ 0.693, an investment at 4% doubles in about 72 / 4 = 18 years.
Why does monthly dollar-cost averaging maximize compounding?
It smooths market timing risk while consistently channeling dividends and interest into additional principal, allowing geometric compounding to accelerate over decades.
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All processing happens in your browser. Your files are never uploaded.
Verified: Known cases, a 0% rate, error states and the yearly table are covered by browser tests
Did you know?
Under compounding, gains generate their own gains, so growth accelerates with time. By the rule of 72, at 3% a year the principal doubles in about 24 years.