Last updated: September 16, 2026
Compound Interest Calculator
See what monthly investing becomes over decades — 401(k), SIP & brokerage.
Your investment plan
Assumes monthly compounding at a fixed rate, before taxes and fees. Educational estimate, not financial advice.
Projected value
$106,639.02
after 10 years
You invest
$70,000.00
Growth
$36,639.02
Growth over time
Why Compound Growth Decides Retirements
Invest $500 monthly at 7% for 30 years and you contribute $180,000 but end with over $600,000 — growth does most of the work. Start ten years later and you must roughly double the monthly amount for the same result. Time in the market beats timing the market because compounding is exponential, not linear.
Use the chart above to feel this viscerally: drag the rate slider between 5% and 9% and watch decades of outcomes fan out. Then try the mortgage calculator to see the mirror image — how the same math works against borrowers — or the loan EMI calculator for auto and personal loans.
Exact Bank Math
Monthly-compounding formulas, verified to the cent.
Private Figures
Salary-scale numbers never leave your browser.
Instant Answers
Every slider move recomputes live. No forms, no spam calls.
Frequently Asked Questions
How does compound interest work?
Returns earn returns: each period your gains join the balance and earn the next period too. Over decades this snowball dominates — most of a 30-year portfolio is growth, not contributions. The chart above shows both curves separating over time.
What return rate should I assume?
US stocks averaged ~10% nominal (~7% after inflation) long-term. Use 6-7% for realistic planning, 4-5% for conservative plans. The slider makes sensitivity obvious: small rate changes compound into life-changing differences.
Is this a SIP calculator?
Yes — set the starting amount to 0 and enter your monthly SIP contribution. The math (monthly compounding with periodic investments) is identical across SIPs, 401(k)s, and brokerage accounts.
Monthly vs yearly contributions — does it matter?
Slightly: monthly contributions compound a touch faster since money enters earlier. This calculator compounds monthly, matching real SIP and 401(k) behavior.
Does it account for taxes and fees?
No — results are pre-tax and fee-free. A 1% annual fee can erase roughly a quarter of 30-year gains, so treat projections as ceilings and confirm with an advisor for real planning.
Is my investment data private here?
Completely. All math runs locally in your browser — figures never leave your device, are never stored, and are never tracked.
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