Compound interest calculator — see how money grows over time, with monthly contributions, charts, and breakdown.
- Runs locally
- Category Calculator
- Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.
| Year | Start balance | Interest | Contributions | End balance |
|---|---|---|---|---|
| 1 | $10,000 | $1,382 | $6,000 | $17,382 |
| 2 | $17,382 | $2,155 | $6,000 | $25,538 |
| 3 | $25,538 | $3,009 | $6,000 | $34,547 |
| 4 | $34,547 | $3,953 | $6,000 | $44,499 |
| 5 | $44,499 | $4,995 | $6,000 | $55,494 |
| 6 | $55,494 | $6,146 | $6,000 | $67,640 |
| 7 | $67,640 | $7,418 | $6,000 | $81,058 |
| 8 | $81,058 | $8,823 | $6,000 | $95,881 |
| 9 | $95,881 | $10,375 | $6,000 | $112,257 |
| 10 | $112,257 | $12,090 | $6,000 | $130,346 |
| 11 | $130,346 | $13,984 | $6,000 | $150,331 |
| 12 | $150,331 | $16,077 | $6,000 | $172,407 |
| 13 | $172,407 | $18,388 | $6,000 | $196,796 |
| 14 | $196,796 | $20,942 | $6,000 | $223,738 |
| 15 | $223,738 | $23,763 | $6,000 | $253,501 |
| 16 | $253,501 | $26,880 | $6,000 | $286,381 |
| 17 | $286,381 | $30,323 | $6,000 | $322,704 |
| 18 | $322,704 | $34,127 | $6,000 | $362,831 |
| 19 | $362,831 | $38,328 | $6,000 | $407,159 |
| 20 | $407,159 | $42,970 | $6,000 | $456,129 |
| 21 | $456,129 | $48,098 | $6,000 | $510,227 |
| 22 | $510,227 | $53,763 | $6,000 | $569,990 |
| 23 | $569,990 | $60,020 | $6,000 | $636,010 |
| 24 | $636,010 | $66,934 | $6,000 | $708,944 |
| 25 | $708,944 | $74,571 | $6,000 | $789,515 |
| 26 | $789,515 | $83,008 | $6,000 | $878,522 |
| 27 | $878,522 | $92,328 | $6,000 | $976,850 |
| 28 | $976,850 | $102,624 | $6,000 | $1,085,474 |
| 29 | $1,085,474 | $113,998 | $6,000 | $1,205,473 |
| 30 | $1,205,473 | $126,564 | $6,000 | $1,338,037 |
What this tool does
Free compound interest calculator with everything a serious saver, investor or student of personal finance actually needs: enter principal, annual rate, term in years, and a compounding frequency (annually, semi-annually, quarterly, monthly or daily), optionally add a monthly contribution, and read off the final value, total invested, total interest and overall return in one shot. A year-by-year breakdown shows starting balance, interest earned, contributions added and ending balance for every single year — the same table mutual fund prospectuses print, but live, editable and instant. An inline SVG growth curve plots total value against money-in so you can literally see the gap between what you put in and what compounding gives back open up. Three one-click scenarios are baked in: Warren Buffett's 19% over 50 years on a $10k seed, the S&P 500's long-run 10% over 30 years with $500 monthly contributions, and a conservative 2% money-market account over 10 years. Everything runs 100% in your browser — your numbers never leave the device, there is no signup, no log, no ads on the calculation. Built for retirement planners, FIRE crowd, parents running 529-style college math, students learning the time value of money, and anyone who wants to settle the question "is starting now actually worth it" with real numbers instead of vibes.
Tool details
- Input
- Numbers
- The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
- Output
- Live result + Preview
- The result area focuses on usable output, with copy, download, or preview actions when supported.
- Privacy
- Browser-side processing
- The main tool logic does not call an external API, so inputs normally stay in the current tab.
- Save / share
- No account required
- Open the page and use it; whether results survive refresh depends on the tool.
- Performance budget
- Initial JS <= 25 KB
- No WASM budget is declared, keeping the tool quick to open on mobile.
- Best fit
- Calculator · Marketer
- Category and role tags drive related tools, internal links, and quick fit checks.
How to use
-
1. Input
Paste or drop your content into the tool panel.
-
2. Process
Click the button. All processing is local in your browser.
-
3. Copy / Download
Copy the result or download to disk in one click.
How Compound Interest Calculator fits into your work
Use it for fast estimates, comparisons, and planning numbers before you make the final call.
Calculation jobs
- Getting a realistic range before a purchase, plan, workout, or schedule decision.
- Comparing scenarios by changing one input at a time.
- Turning rough assumptions into a number you can discuss.
Calculation checks
- Double-check units, dates, rates, and rounding assumptions.
- Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
- Save the inputs that produced an important result so you can reproduce it later.
Good next steps
These links move the current task into a more complete workflow.
- 1 Expense Tracker Expense tracker — log spend, categorize, see monthly totals, all in your browser. Open
- 2 ROI Calculator ROI %, net gain, annualized ROI (CAGR) and payback period — one screen, share a link — 100% in your browser Open
- 3 Mortgage Calculator Mortgage calculator — monthly payment, total interest, amortization schedule, early payoff scenarios. Open
Real-world use cases
Deciding whether to start your 401(k) at 25 or wait until 30
You make $60k and can spare $500 a month. Plug in $0 principal, 8% nominal, 40 years and $500 monthly: starting at 25 you reach about $1.55M by 65. Push the start to 30 (35 years left) and you land near $1.03M. Those five delayed years cost roughly $520k, far more than the $30k you would have contributed in them. The chart makes the gap visceral before you decide.
Sizing a 529 college fund for a newborn
You want about $200k ready in 18 years. Try $10,000 seed, 6% annual, 18 years, $400 monthly: the breakdown table shows you crossing $190k right around year 18, with interest overtaking contributions near year 12. If 6% feels optimistic, drop to 4% and watch the monthly number you need climb to roughly $600 to hit the same target.
Comparing a 2% savings account against an index fund
Load the 2% money-market preset, then the S&P 500 10% preset, and read the final values side by side. On $10,000 over 30 years the gap is brutal: about $18,100 at 2% versus about $174,000 at 10%, before any monthly contribution. Seeing both totals in plain dollars settles the "is the risk worth it" argument better than any percentage ever does.
Stress-testing a FIRE plan against a bad-returns decade
Your spreadsheet assumes 7% real forever. Run it once at 7% and once at 4% over your 22-year horizon with your real monthly savings. If the 4% run still clears your number, the plan survives a flat decade. If it falls short by $300k, you learn now that you need a higher savings rate or a longer timeline, not at 55 when it is too late to fix.
Common pitfalls
Typing 5% as 5 instead of 0.05 conceptually — this tool wants the percent (5), but if a field looks off, check whether you entered 500% by accident; a $10k stake "growing" to $9M in 10 years is the tell.
Mixing up annual rate with monthly rate. If your bank quotes 0.5% per month, enter 6% annual with monthly compounding, not 0.5% annual — otherwise you understate growth twelve-fold.
Forgetting that the monthly contribution keeps running every year. Entering $500/month over 30 years means $180k of contributions, not a one-time $500; if total invested looks huge, that is why, not a bug.
Privacy
Every number you type — principal, rate, term, monthly contribution — is computed entirely inside your browser tab. Nothing is sent to a server, no telemetry fires on the values, and there is no log. The inputs are not written into the URL either, so a link you share never carries your actual savings figures. Close the tab and the data is gone.
FAQ
Tool combos
Folks in your role tend to reach for these alongside this tool.
- Age Calculator Calculate your exact age — years, months, days, hours. Compare two dates or count to a future date.
- AI Model Comparison AI model comparison — 20+ models (GPT / Claude / Gemini / Llama / Qwen) across price, context, speed, capabilities (2026).
- Avatar Generator Generate avatars from initials, identicons, or random shapes. Download PNG/SVG.
- Barcode Generator Code 128 / EAN-13 / UPC-A / Code 39 — generate scannable 1D barcodes, export SVG or PNG, fully offline.