Compound Interest Calculator
Project how savings or an investment grow with compound interest, monthly contributions, fees, and tax. Runs in your browser, no signup. Educational estimate.
| Year | Start of year | Contributions | Growth | Fees | End of year |
|---|---|---|---|---|---|
| 1 | 10,000 | 6,000 | 925 | 0 | 16,925 |
| 2 | 16,925 | 6,000 | 1,410 | 0 | 24,335 |
| 3 | 24,335 | 6,000 | 1,929 | 0 | 32,264 |
| 4 | 32,264 | 6,000 | 2,484 | 0 | 40,747 |
| 5 | 40,747 | 6,000 | 3,077 | 0 | 49,825 |
| 6 | 49,825 | 6,000 | 3,713 | 0 | 59,538 |
| 7 | 59,538 | 6,000 | 4,393 | 0 | 69,930 |
| 8 | 69,930 | 6,000 | 5,120 | 0 | 81,051 |
| 9 | 81,051 | 6,000 | 5,899 | 0 | 92,949 |
| 10 | 92,949 | 6,000 | 6,732 | 0 | 105,681 |
| 11 | 105,681 | 6,000 | 7,623 | 0 | 119,304 |
| 12 | 119,304 | 6,000 | 8,576 | 0 | 133,880 |
| 13 | 133,880 | 6,000 | 9,597 | 0 | 149,477 |
| 14 | 149,477 | 6,000 | 10,689 | 0 | 166,165 |
| 15 | 166,165 | 6,000 | 11,857 | 0 | 184,022 |
| 16 | 184,022 | 6,000 | 13,107 | 0 | 203,129 |
| 17 | 203,129 | 6,000 | 14,444 | 0 | 223,573 |
| 18 | 223,573 | 6,000 | 15,875 | 0 | 245,448 |
| 19 | 245,448 | 6,000 | 17,407 | 0 | 268,855 |
| 20 | 268,855 | 6,000 | 19,045 | 0 | 293,900 |
Educational estimate only, not investment, tax, pension, or financial planning advice. Future returns are not guaranteed. Fees, taxes, inflation, the product type, and the chosen investment track can change the actual result. Consult a suitable professional before any financial decision.
This compound interest calculator doubles as an investment growth calculator and a savings calculator with monthly contributions. Enter an initial amount, a monthly contribution, an estimated annual return, and a number of years, and you get a final amount, the split between what you put in and what you earned, an optional fee and capital gains tax estimate, and a year-by-year breakdown. Compound interest means earnings build not only on the original principal but also on the gains already accumulated, so growth accelerates the longer money stays invested. Everything runs in your browser: there is no signup, no account, and nothing you type is uploaded or stored. The same inputs always produce the same numbers (the math is deterministic). This is an educational estimate, not financial advice, and future returns are never guaranteed. Last updated: May 2026.
How to use this tool
- 01Enter the initial amount and monthly contributionType how much you already have and how much you plan to add each month. Either one can be left at 0. The currency is up to you; the tool treats the numbers as plain amounts.
- 02Set the annual return and number of yearsEnter an estimated annual return as a percentage and the number of years, then choose monthly or yearly compounding. You can also set an optional annual fee and a capital gains tax rate.
- 03Read the projection and breakdownYou get the final amount, total contributions, profit, estimated tax, a visual contributions-vs-profit bar, and a year-by-year table showing the balance at the start, contributions, growth, fees, and the end-of-year balance.
When is this useful?
- Planning retirement or long-term savingsSee how a steady monthly amount can grow across decades, and how starting earlier or adding a few more years changes the final number dramatically.
- Comparing investment scenariosChange the return, contribution, or time horizon to compare conservative and optimistic assumptions side by side before committing to a plan.
- Understanding regular monthly investingSee how much of the final balance comes from your own contributions versus accumulated compound growth, which makes the effect of consistency easy to grasp.
Examples
- 10,000 + 500/month, 7%, 20 yearsA modest starting amount with a steady monthly contribution grows substantially over 20 years because each year compounds on the previous one.
- 0 initial + 1,000/month, 5%, 10 yearsWith no starting balance, monthly contributions alone accumulate into a meaningful sum within a decade.
- 50,000 initial, no contributions, 6%, 15 yearsA one-time lump sum that grows on its own demonstrates pure compounding on a single principal with no new deposits.
Tips for a better result
- Time is the strongest factorThe longer the horizon, the larger the compounding effect. A few extra years often changes the result more than a slightly higher return does.
- Higher return means higher riskA higher assumed return also implies higher risk. Do not treat any return as guaranteed; test more conservative figures too.
- Small fees compound against youAn annual fee is deducted from the balance every period, so over many years even a small percentage can meaningfully reduce the final amount. Try toggling the fee to see its impact.
What is compound interest?
Compound interest is when earnings accrue on previously accumulated gains, not just on the original principal. Instead of growing by a flat amount each period, the balance grows at an accelerating pace as time passes. This is why an early start and consistency over many years have such an outsized effect on the final result.
How compounding frequency affects the result
With monthly compounding, the annual return is converted to an equivalent monthly rate ((1 + r)^(1/12) - 1) and contributions are added and grown each month, so the result is usually slightly higher. With yearly compounding, contributions for the year are added and growth is applied once per year. The same nominal annual rate produces a modestly larger final balance under monthly compounding because gains start earning sooner.
How fees and taxes change the outcome
The optional annual fee is deducted from the balance each period, reducing the base that compounds going forward, so its effect grows over time. The capital gains tax is applied only to positive profit (final amount minus total contributions), never to the contributions themselves. The calculator uses the single tax rate you enter; real-world taxation depends on the product, jurisdiction, exemptions, and rules, so treat the tax figure as a rough estimate.
How the calculator works
The math is a standard compound-interest model based purely on the assumptions you enter. There is no connection to any financial institution and no market data is fetched. Contributions, growth, fees, and tax are computed step by step and shown in the year-by-year table. The same inputs always yield the same outputs.
Privacy
Everything happens locally in your browser. The amounts, rates, and results are never uploaded, never saved to localStorage or IndexedDB, and never sent to analytics. Minimal operational analytics measure only general usage such as a page view and a first successful use; no value or result is ever transmitted. Refreshing the page resets the inputs to defaults.
Disclaimer
This is an educational estimate only and not investment, tax, pension, or financial planning advice. Future returns are not guaranteed. Fees, taxes, inflation, the product type, the chosen investment track, and applicable exemptions can change the actual outcome. Consult a suitable professional before making any real financial decision.
Frequently asked questions
What is compound interest?
Earnings that accumulate on previously earned gains as well as on the original principal. Because of this, the balance grows at an accelerating rate the longer it stays invested.
How does this work as an investment growth calculator?
Enter what you have today, an estimated annual return, and a time horizon, and it projects how the investment could grow year by year through compounding. It is a planning estimate based on the assumptions you provide, not a forecast of any specific market or product.
Can I include monthly contributions?
Yes. Add a recurring monthly contribution and the calculator works as a savings calculator with monthly deposits: each contribution is added on its schedule and then compounds alongside the rest of the balance. You can see how much of the final amount comes from your deposits versus accumulated growth.
Can I use it as a future value calculator for a lump sum?
Yes. Leave the monthly contribution at 0 and enter only an initial amount to project the future value of a single lump sum growing on its own at the rate and horizon you set.
Does it fetch live interest rates or market data?
No. There is no connection to any bank, broker, or market feed. The projection is based purely on the return rate and assumptions you type in, so you control every figure.
How does compounding frequency affect the result?
Monthly compounding adds and grows money each month, so gains start earning sooner and the final amount is usually slightly higher than with yearly compounding at the same nominal annual rate.
Do fees and taxes change the result?
Yes. The annual fee is deducted from the balance each period, which reduces the amount that keeps compounding. The capital gains tax applies only to positive profit, not to your contributions. Both are optional and based on the figures you enter.
Is the result guaranteed?
No. It is an educational estimate based on the assumptions you provide. Future returns are not guaranteed and the actual result may differ significantly.
Is the tax calculation exact?
No. Tax is applied in a simplified way to profit only, using the single rate you enter (default 25%). Real taxation depends on the product, jurisdiction, exemptions, and benefits, and can differ.
Is any of my data uploaded?
No. All calculations run in your browser. No amount, rate, or result is uploaded, stored, or sent to analytics.
Which currency does it use?
It is currency-agnostic. The English version shows no currency symbol, so you can read the numbers in whatever currency you have in mind. Only the formatting (comma thousands separators) is applied.
Is this financial advice?
No. This is an educational estimate, not investment, tax, pension, or financial planning advice. Consult a suitable professional before making any financial decision.
Is the tool free?
Yes. It is free, with no signup, no account, and no reasonable usage limit.
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