Compound Interest

Why this calculator matters

Einstein didn’t actually call it the 8th wonder, but the math feels like it. $10k alone at 8% for 20y becomes $49k. Add $500/mo and it becomes $343k — 70% is earnings.

Numbers beat narratives. Move a single slider — return 8%→10%, years 20→25, monthly 5k→7k — and the left side answers instantly. That instant feedback is the whole product: you don’t need a spreadsheet, you need a feel for the trade-off.

Formula — the exact math we run

Net = return − fee (if you entered a fee). Real = nominal / inflation. n = 12 for monthly, 4 for quarterly, 1 for yearly, 365 for daily. All money fields follow the currency you pick in the header.

Try this example — verify it yourself

What each input actually does

• Starting amount: one-time capital. Small but early beats large but late.
• Monthly / yearly amount: the habit. For 20+ year horizons, this input drives >60% of the final number.
• Return & inflation: nominal lies, real tells the truth. Use real = nominal − inflation for planning. Conservative real for India is 7–8% for equity, 2–3% for debt.
• Years & compounding: years is the exponent. Frequency matters <1% vs monthly; fee matters 20–30%.
• Advanced: frequency, inflation, fee. Fees look tiny (0.5%) but are charged on a growing balance — that’s why they snowball.

What the outputs mean

• Final / corpus: what the account shows.
• Invested: what you put in.
• Gain / interest / earnings: the difference — the part that did no extra work.
• Real (inflation-adjusted): what it buys today. Compare real across decades, not nominal.
• Chart & table: hover the chart, audit the table. The gap between the two lines is your compounding; when it widens fast, you’re in the good part.

Assumptions — where it can be wrong

• Constant return — markets aren’t. This is a median path.
• No extra withdrawals, no missed contributions, on-time compounding.
• Taxes/fees only if you entered them. For taxable, either lower the return or add the fee.
• Currency symbols change formatting, not the amount — 5000 means 5000 in the selected currency.

Make it useful — 30-second tests

• Slider test: move return 8→12→6 and years 15→25. Notice how 6% at 25y beats 12% at 15y — time > rate.
• Fee test: set fee 0→1% and watch 30y corpus drop 25–30%. Then switch to a 0.1% fund.
• Switch test: use the top “Switch” dropdown to hop to a related calculator without going home — compare lumpsum vs SIP for the same goal.
• Share test: copy the URL after tuning — send it to a friend; they see your exact sliders and chart.

Common questions

Is this private? Yes. All math runs in your browser; we never see your numbers. The URL stores the inputs, not a server.

How close to reality? Formula-accurate, assumption-dependent. Use conservative real returns and round down for planning.

Can I see the steps? Yes — the yearly table shows Invested vs Balance row by row. The difference is earnings; its growth rate is the compounding.

Does changing currency convert? No — it only changes the symbol/formatting. 5000 means 5000 in that currency.

Can I export? Where you see Export CSV (SIP, PPF, etc.), it exports the exact schedule. Else copy the share URL.

When does a fee matter most? Always, but especially long horizons and large balances — that’s when the base for the fee is biggest.

When to use this vs the other calculators

How much will my habit be worth at retirement? Should I pay 1% fee? What does 3% inflation do to ₹1Cr?