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Compound interest tools and guides

Compound Interest Tools and Simple Guides

Use the main calculator for accurate long-term growth estimates, then explore the guides that explain how compounding, frequency, inflation, and regular contributions change the result.

Accurate contribution mathMonthly deposits are handled with period-by-period growth.
Built for comparisonChange rate, time, and compounding frequency in seconds.
Plain-English guidesLearn the formula without getting buried in jargon.
Start with the main tool

Compound interest calculator

Best page for investors and savers who want a final value, total contributions, and total interest earned.

Open the full calculatorSupports monthly contributions, compounding frequency, and year-by-year breakdowns.
Plan your monthly amountEstimate the monthly contribution needed to reach a target balance. Estimate time to 100kWork out how long it could take to reach a common milestone. See beginner examplesUnderstand compounding through simple worked scenarios.

Where to begin

Calculate growthModel principal, rate, time, compounding frequency, and recurring deposits. Compare modelsSee when compound interest and simple interest produce different outcomes. Check real growthUnderstand why inflation can quietly reduce purchasing power.

Popular scenario pages

Use these example-based pages if you want to sanity-check common contribution and lump-sum cases before entering your own numbers.

$100 a month for 10 yearsSee a simple beginner contribution scenario.$100 a month for 30 yearsUnderstand why time changes the picture.$500 a month for 20 yearsCompare a larger monthly investing habit.$1,000 at 5% for 10 yearsA clean lump-sum baseline example.$10,000 at 7% for 30 yearsSee what long-horizon compounding can do.How long to double at 7%Compare the Rule of 72 with exact math.

Browse by starting amount or target

Use these pages when you think in concrete money goals, not just rates or years.

Compound interest on $5,000Small starting amount example.Compound interest on $50,000See how a stronger starting balance grows.Compound interest on $100,000Six-figure capital planning page.How to reach $500kMilestone planning guide.How long to reach $500kEstimate the time side of the goal.How to reach $1 millionTranslate a big goal into a long-term plan.

Browse by return rate or time horizon

These landing pages target highly specific searches and make it easier to compare one assumption at a time.

5% compound interestConservative planning scenario.7% return calculatorCommon long-term assumption.10-year compound interestMedium-term projection page.20-year compound interestLong-horizon comparison.30-year compound interestRetirement-style time frame.8% return calculatorHigher-return comparison case.

Retirement and FI pages

These pages extend the site into retirement planning, coast FIRE, and age-based investing questions.

Retirement compound interestProject a balance by retirement age.How much will I have at 65?Age-based projection calculator.Financial independence calculatorEstimate years to an FI target.Coast FIRE calculatorCheck the balance needed today to coast.$100/month from 25 to 65Small monthly amount over a long horizon.$500/month from 30 to 60Larger monthly amount over 30 years.

Retirement income and inflation

These are the last truly necessary support pages before you stop building and start measuring signals.

4% rule calculatorTurn annual spending into a portfolio target.Safe withdrawal rateCheck what your spending implies today.Retirement in today's dollarsAdjust a future target for inflation.Lean FIRE vs Fat FIREUnderstand why spending assumptions drive the target.