Compound Interest & DCA Calculator
Work out what regular investing adds up to — initial sum, monthly or yearly contributions, a chosen rate basis, and inflation-adjusted buying power, year by year. Nothing you type leaves your browser.
Also available as a desktop app for Windows.
About this tool
Compound growth is easy to state and hard to feel. A thousand a month at 7% for thirty years puts roughly 1.18 million on the table, of which only 360,000 came out of your pocket — but the same sum at 5% gives about 819,000, and at 3% about 580,000. Two percentage points, and 357,000 of difference. That is why this tool shows the rate you entered as an actual per-period number instead of hiding it behind the annual figure.
It also refuses to be vague about two things most calculators leave open. The rate basis: an "effective annual rate" of 7% really does grow 7% a year, while a "nominal annual rate" of 7% compounded monthly grows 7.23% — on the thirty-year example above those two readings differ by about 51,000. And the timing of contributions: money paid in at the start of each period earns that period’s return, money paid at the end does not.
Finally it does the arithmetic in both directions. Set a target and it tells you what to contribute each period, or how long your current contributions would take. Inflation is applied as real discounting, so the "in today’s money" figure is the one to compare against prices you actually recognise.
Frequently asked questions
- What is the difference between the balance and "in today’s money"?
- The balance is the nominal number — what the account statement would say. "In today’s money" divides it by cumulative inflation, giving what that sum could buy at today’s prices. At 3% inflation over 30 years, buying power falls by about 59%, so a nominal 1.18 million is worth roughly 485,000 in today’s terms. Comparing a future nominal figure against today’s prices is the single most common way people overestimate an investment.
- Effective annual rate or nominal annual rate — which should I use?
- Use the effective rate when you mean "the money actually grew by this much over a year", which is usually what people mean by an annual return. Use the nominal rate when a product quotes it that way, typically with a compounding frequency attached — a nominal 6% compounded monthly is 6.17% effective. The tool defaults to effective because that reading is the more conservative one and the more commonly intended.
- Should contributions be at the start or the end of the period?
- Start, if you invest on a fixed day each month and the money is in the market from then on — the usual case for automatic monthly investing. End, if you are modelling contributions made at the very end of each period. The start-of-period choice earns one extra period of return per contribution: with monthly investing that is about 0.6% more in total over 30 years, while with yearly contributions the gap is the full annual rate — nearer 7%.
- Does this account for fees and taxes?
- No, and deliberately not — fund fees, platform charges and taxes vary far too much between countries and products for one number to be honest. Enter your return net of fees and taxes and the projection stays correct. A 1% annual fee on the 30-year example above cuts the final balance by about 17%, which is worth checking against your own product.
- Which currency are the amounts in?
- Any. The calculator works with plain numbers and never assumes a currency, symbol or exchange rate — so it behaves identically for yuan, dollars, euros or anything else. The only formatting that changes with language is the thousands and decimal separator.
- Does it send my numbers anywhere?
- No. Every calculation is plain arithmetic in the page. There is no server, no request and no logging, and the tool keeps working with the network switched off — a practical way to verify the claim yourself.