Compound Interest Calculator
See how a starting balance and monthly contributions grow over time, with a year-by-year breakdown of interest earned.
- Free, no account
- No watermark
- No usage limit
About the Compound Interest Calculator
Most compound interest calculators do one thing well. They show a balance getting bigger. Fine for the years you're saving, no help at all the day you want to live off the money. This one covers both ends, and the spending end is the one people actually worry about. Turn on withdrawals and it draws the balance down on a schedule while whatever is left keeps compounding, and if you're pulling out too much it names the year the money runs dry. It also shows what your big final number is really worth in today's dollars once inflation takes its cut. Free, runs in your browser, and every field is live, so $1,000 at 5% for 10 years lands at $1,647.01 the moment you type it and the chart redraws as you go.
How to use
- Start with your principal. The starting amount is whatever you have today. It can be $0 if you're building from nothing and letting deposits do the work.
- Add a contribution if you plan to keep saving. Type the amount, then flip the /month or /year toggle. Leave it at 0 for a pure lump sum.
- Set the rate. Type a percentage like 5 or 7.5, or tap one of the 4, 5, 7, 10 quick buttons. Zero is allowed and just shows your deposits with no growth, useful as a baseline.
- Choose how often it compounds, anywhere from daily to continuously. Most savings accounts and CDs credit interest daily or monthly.
- Enter the years, or tap 10, 20, 30. You get the final balance, what you actually put in, total interest, and the effective yield (APY), plus a growth chart and a year-by-year table.
- Open More options for the rest: deposit timing, a yearly raise to your contributions, withdrawals, and an inflation rate.
Landed on a scenario you like? Copy summary gives you a one-line result, Download CSV saves the full schedule, and Share builds a link that reopens the exact setup for a partner or your future self.
Deposits, and the moment interest passes you
A lump sum growing on its own is the textbook example. Almost nobody actually builds wealth that way. You add money month after month, and those steady deposits are what build the balance up over the years. Set the starting amount to $0, put $500 in the contribution box on /month, and run 7% for 30 years. The balance at the end lands around $609,985, of which you only put in $180,000. The rest, roughly $430,000, is interest the account earned on itself.
There's one field almost no free calculator includes. Open More options and set "Increase deposit yearly" to 3%, about a normal annual raise. Your contribution creeps up as your income would, and the ending balance climbs to about $833,580, all of it coming from one small yearly nudge.
The chart makes all of this legible. The lower band is your own cash, principal plus deposits. Everything above it is interest. Early on the interest band is a sliver. Somewhere in the middle it crosses over and starts outgrowing everything you've put in, and from that point the account is doing more of the work than you are. Hover any year to read the exact split, or open the year-by-year table to watch the annual interest climb even while your deposit holds flat.
The phase most calculators quit before: pulling money out
Watching a balance grow is only half the question. The other half, whether that balance actually lasts once you start living off it, is the part most compound tools refuse to touch. The withdrawal field in More options handles it, the way a compound calculator should have all along. It draws the balance down on your schedule, monthly or yearly, while everything still invested keeps earning.
Retire with $500,000 at 5% and pull $2,500 a month for 25 years. You take out $750,000 over that stretch, more than you started with, and still finish near $251,871, because the balance kept compounding the whole way. Push the withdrawal too high and it goes the other way. Try $4,000 a month on that same $500,000 and the calculator flags it, the balance empties in year 15 and every month after that pays out only what is left, which by then is nothing. Catching that shortfall is the reason the feature exists, since it shows exactly how much is too much and lets you lower the withdrawal before a real plan depends on it.
It won't replace a proper retirement planner, employer matches and variable returns and tax rules all live over there. For a quick read on "can this actually last," though, it beats building a spreadsheet from scratch.
What that final number is actually worth
A big projected balance can be misleading until you adjust it for inflation. Add an inflation rate under More options and the tool shows a second figure, the same balance in today's buying power. That $609,985 at 7% over 30 years is worth about $290,806 in current dollars if inflation runs 2.5%, less than half of the headline number. So aim well above inflation, and go by the inflation-adjusted figure rather than the raw one.
Fees work in the opposite direction. Because a fee is charged on your balance every year, its cost also compounds over the years, steadily reducing what you keep. Drop a $100,000 investment from an 8% return to 7%, which is roughly what a single 1% annual fee costs you, and over 30 years you go from about $1,093,573 to $811,650. That's around $282,000, gone to one percentage point. The tool doesn't model fees on its own, but you can see the effect yourself, just run your rate, then run it a point lower and compare. The same trick works for testing an optimistic return against a cautious one.
Frequently asked questions
What interest rate should I actually put in?
Depends what you're modeling. A broad US stock index has averaged roughly 10% a year before inflation over long stretches, but that's a rough average across some brutal down years, not a promise. Bonds tend to run lower, often 3 to 5%. High-yield savings and CDs drift with the times. For long-range planning a lot of people pencil in 6 to 7% for stocks to stay honest. When you're unsure, run it once optimistic and once pessimistic, then plan around the lower one.
Is chasing a daily-compounding account worth it?
Barely, because the compounding frequency matters far less than the rate itself. Take $10,000 at 8% for 10 years: annual compounding gives $21,589, daily gives $22,253. Going from once a year to every single day adds about $664 over the whole decade, roughly 3% of the balance. Half a point of extra rate outweighs any gain from compounding more often, so an account paying 4.5% compounded yearly still comes out ahead of one paying 4% compounded daily. Compare the rate first and treat the compounding schedule as a tiebreaker.
Why is the APY higher than the rate I typed?
Because APY counts the compounding. Your typed rate is the nominal headline, and APY is what you actually keep once interest starts earning interest within the year. A 5% rate compounded monthly works out to an APY of 5.12%. It's the fair way to line up savings accounts, since one bank's 4.95% compounded daily can beat another's flat 5% compounded once a year. The calculator shows it on the "Effective annual yield" line.
Can I use this for a 401k or IRA?
For the core projection, yes. A fixed return plus steady monthly contributions plus a yearly raise is what a retirement account looks like from a distance, so set your contribution, add the raise, and pick a cautious rate. What it leaves out on purpose is employer matching, contribution limits, and the tax treatment. A Roth is funded with after-tax dollars and later comes out tax-free, whereas a traditional 401k gives you the deduction now and taxes the withdrawals in retirement. Once the shape looks right here, move to a dedicated retirement calculator for those details.
How is compound interest different from simple interest?
Simple interest only ever pays on your original principal. Compound interest pays on the principal and on the interest already earned, so it feeds itself. Over a year or two they're close. Over decades they're not in the same league, $1,000 at 5% for 30 years reaches about $4,322 compounding once a year against just $2,500 as simple interest. The longer the money sits untouched, the wider that gap opens.
My number doesn't match another calculator. Why?
Almost always the deposit timing or the compounding frequency. This tool credits deposits at the end of each period by default and compounds at whatever you selected. A calculator that deposits at the start of the period, or compounds annually when you assumed monthly, will land a little higher or lower. Match those two settings and the results line up, the leftover gaps are usually just rounding.
Does anything I type get uploaded?
No. Every calculation happens on your own device, there are no network calls, and nothing is logged or stored on a server. The Share link and the CSV are built from your numbers locally, and the three amounts in a Share link, your starting balance and what you put in and take out, sit after the # in it, the part a browser never sends to a server. It keeps working offline once the page has loaded, and it quietly remembers your last setup in this browser so a return visit picks up where you stopped.