What it does
Compound interest means you earn interest on the interest you already earned. Over a few years the effect is small; over twenty or thirty it is large. This calculator shows what a start amount plus regular deposits will grow to, how much of that is your own money and how much is interest.
You can add a yearly fee (many funds and accounts charge one) and a yearly inflation figure, so you also see what the final amount is worth in today’s money. To plan the deposits themselves, try the budget planner; to see how prices change over time, the inflation calculator.
How to use it
- Pick your currency and type the Start amount (it can be 0).
- Enter a Regular deposit, and choose whether you pay it every month or every year, at the start or the end of that period.
- Enter the Interest rate, how often interest is added, and the Years.
- Optionally add a Yearly fee and Inflation.
- Read the result cards, the chart and the Year by year table. Download the table as a CSV file for a spreadsheet.
What each setting does
- Interest added: how often interest is credited. Daily or monthly gives slightly more than yearly at the same rate.
- Deposit at the start or end: a deposit at the start of a period earns interest for that period; one at the end does not.
- Yearly fee: taken off the balance a little each month, like a fund’s ongoing charge.
- Inflation: the “In today’s money” figure divides the final balance by the price rise over the years.
- Rule of 72: 72 divided by your rate (after fees) is roughly the years needed to double your money.
Worked example
You put in 1,000 at 5% a year with no deposits. Interest added yearly, it becomes 1,628.89 after 10 years. Added monthly, it becomes 1,647.01. Now add 100 a month: you put in 13,000 in total, and the interest part grows much larger than from the start amount alone.
FAQs
Why is my bank’s figure a little different? Banks may add interest on a different day, round each month, or pay a rate that changes. This tool assumes one fixed rate for the whole time.
Is the return guaranteed? No. Shares and funds go up and down. Use a cautious rate and test a few values.
Does it include tax? No. Interest may be taxable where you live. Not financial or tax advice.
What does a fee of 1% do? Over 30 years, a 1% yearly fee can take a large share of the final amount. Try it and compare.
Where the numbers come from
- Standard compound interest formula, FV = P(1 + r/m)^(m t). Checked against the textbook example: 1,000 at 5% for 10 years is 1,628.89 compounded yearly and 1,647.01 compounded monthly. Rule of 72 is a common rule of thumb.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-10.