Compound Interest Calculator
Ten compounding frequencies, a deposit schedule of its own, tax and inflation — or solve for the principal, rate or time needed. All in your browser.
Final amount: 1,628.89 Total interest: 628.89
| Year | Deposits | Interest | Balance | Total paid in |
|---|---|---|---|---|
| 1 | 0 | 50 | 1,050 | 1,000 |
| 2 | 0 | 52.5 | 1,102.5 | 1,000 |
| 3 | 0 | 55.13 | 1,157.63 | 1,000 |
| 4 | 0 | 57.88 | 1,215.51 | 1,000 |
| 5 | 0 | 60.78 | 1,276.28 | 1,000 |
| 6 | 0 | 63.81 | 1,340.1 | 1,000 |
| 7 | 0 | 67 | 1,407.1 | 1,000 |
| 8 | 0 | 70.36 | 1,477.46 | 1,000 |
| 9 | 0 | 73.87 | 1,551.33 | 1,000 |
| 10 | 0 | 77.57 | 1,628.89 | 1,000 |
🔒 Calculated in your browser — nothing is uploaded. This is a mathematical estimate, not financial advice.
What this calculator shows
Enter a principal, an annual rate and a term in years and months, then choose how often interest is added: once a year, twice a year, every quarter, every two months, every month, twice a month, every two weeks, every week, every day, or continuously — ten choices, named in words rather than as a count of periods, and continuously is the real exponential rather than daily standing in for it. The final amount, the total paid in and the total interest appear as you type; there is no Calculate button to press. Years and months are whole numbers, so half a year typed into Years is refused with a sentence instead of being quietly floored away.
A deposit with a frequency of its own
If you also save a fixed sum, put it in the Deposit box and give it its own frequency — nine of them, from once a year to every day — independent of how often interest is added. A monthly standing order into an account that pays interest daily is an ordinary arrangement, and each deposit is grown from the instant it lands rather than from the end of a compounding period. You can also say whether the deposit falls at the start or the end of its period. Money paid in at the start earns interest for that period as well, which is what a standing order on payday actually does, and over a long term the gap between the two conventions is not small. Once there are deposits, the total interest is split into the part the initial investment earned and the part the deposits earned.
Four questions, not one
The Calculate dropdown chooses which figure is unknown: the final amount, the principal needed, the rate needed, or the time needed. Give a target final amount and the answer comes back as a number — and the table and chart below are then drawn for the plan that reaches the target rather than for the one that was typed. The principal comes out in closed form. A rate and a time have no formula, so they are bisected: 200 halvings of a bracket that is checked first, so a target that cannot be reached is named as unreachable instead of answered with a plausible wrong number. Rates are searched from −99% to 1000%, terms from zero to 200 years.
Tax, inflation and currency
Tax on interest is taken out of every interest payment as it is credited, so what compounds is the after-tax rate, and the tax paid appears as a line of its own. An inflation rate gives the end balance in today’s money. Amounts are plain numbers by default, or formatted in one of twelve currencies — USD, EUR, GBP, JPY, KRW, INR, CNY, CAD, AUD, CHF, BRL, MXN — in the page’s own language. Every input lives in the query string, so a plan worked out here can be sent as a link rather than as a dozen numbers to retype, and one button puts every control back to where it started.
Four views of the same rows
Under the totals: year by year, month by month, bars, or a breakdown. The month rows carry the deposit and the interest for that month, and the year rows are those months added up. The balance chart is drawn from the same rows as the table — so the picture and the numbers cannot disagree — with a dashed line for the money paid in, so the gap between the two lines is the interest. The bars stack the interest on top of what was paid in, one bar per year. The breakdown draws the final amount as a pie of the initial investment, the deposits and the interest, with the three figures beside it. Compounding is slow and then sudden, and the year the curve takes off is the one thing three summary figures can never show. The projection runs to 200 years; the month-by-month table is drawn for terms up to 50 years, and beyond that the page says so rather than printing thousands of rows.
The formula
One unit of money becomes (1 + r/n)^(n·t) after t years at annual rate r compounded n times a year, or e^(r·t) when compounding is continuous. With a tax rate, r is the after-tax rate. The final amount is the principal grown over the whole term plus every deposit grown from its own instant to the end: A = P·g(t) + Σ C·g(t − d). When the deposit frequency and the compounding frequency happen to be the same, that sum collapses to the familiar A = P × (1 + i)^N + C × ((1 + i)^N − 1) ÷ i, where i is the rate per period and N the number of periods — multiplied by a further (1 + i) when the deposit lands at the start of the period. Total interest is the final amount minus everything that was paid in, and buying power is A ÷ (1 + f)^t for an inflation rate f. Figures are shown to two decimals for readability while the underlying math stays exact.
Estimate only, not financial advice
This is a mathematical estimate that assumes a fixed rate and regular compounding. Real accounts and investments involve variable rates, fees, taxes and withdrawals, so actual returns will differ. Use it to compare scenarios and build intuition, not as a guarantee or a substitute for advice from a qualified financial professional.
Frequently asked questions
What formula does this calculator use?
Money grows by (1 + r/n)^(n·t) over t years at annual rate r compounded n times a year, or by e^(r·t) when compounding is continuous. The final amount is the principal grown over the whole term plus each deposit grown from the moment it lands to the end, which is what lets the deposit frequency differ from the compounding frequency. When the two frequencies are the same, that sum is exactly the familiar A = P × (1 + i)^N + C × ((1 + i)^N − 1) ÷ i, with i the rate per period and N the number of periods, times a further (1 + i) if the deposit lands at the start of the period. Total interest is the final amount minus the principal and every deposit.
Can I add regular savings, not just a lump sum?
Yes, and the deposit has a frequency of its own — once a year, twice a year, quarterly, every two months, monthly, twice a month, every two weeks, weekly or daily — set separately from how often interest is added. A monthly deposit into an account that compounds daily is modelled properly: every deposit grows from the instant it lands. You can also choose whether it falls at the start or the end of its period, and the totals split the interest into what the initial investment earned and what the deposits earned.
Why does more frequent compounding give a larger amount?
Each time interest compounds it is added to the balance and starts earning interest itself. Compounding monthly applies this more often than annually at the same nominal rate, so the final amount is slightly higher.
Is anything uploaded to a server?
No. Every calculation runs entirely in your browser with JavaScript. Nothing you type is sent anywhere or stored.
Can it work out the rate or the time I need instead of the final amount?
Yes. The Calculate dropdown has four settings: the final amount, the principal needed, the rate needed and the time needed. Type a target final amount and the missing figure is worked out — the principal in closed form, the rate and the time by bisection over 200 steps (rates from −99% to 1000%, terms from zero to 200 years). The table and the chart are then drawn for the plan that reaches your target. If nothing in that range reaches it, the page says so rather than showing a number.
Does it handle continuous compounding?
Yes, as its own option, computed as e^(r·t) rather than as daily compounding standing in for it. The ten choices are once a year, twice a year, every quarter, every two months, every month, twice a month, every two weeks, every week, every day and continuously.
Can I take tax and inflation into account?
Yes. Tax on interest is deducted from every interest payment as it is credited, so the rate that compounds is the after-tax one, and the tax paid is shown as its own line. An inflation rate adds a buying-power figure: the end balance expressed in today's money, A ÷ (1 + f)^t.
Is there a month-by-month table?
Yes — the Month by month view shows the deposit, the interest and the balance for every month, and the year-by-year rows are those same months added up. It is drawn for terms up to 50 years; for anything longer the page asks you to use the year-by-year view instead of rendering thousands of rows. The projection itself runs to 200 years.
Can I show the result in a currency?
Yes. Plain numbers are the default, or pick one of twelve codes — USD, EUR, GBP, JPY, KRW, INR, CNY, CAD, AUD, CHF, BRL, MXN — and every amount on the page is formatted for that currency in the language you are reading the page in.
Can I share the plan I worked out?
Yes. Every input is kept in the page's address, so the Copy link button gives you a URL that opens the same plan for someone else. A Clear button puts every control back to its starting value.