Enter your savings or investment, sit back, and watch the numbers do the work. Takes 10 seconds.
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What are you calculating?
💰
Growing my savings
Sarah, 25 — $200/mo into an ETF
👶
Saving for my child
Mark & Lisa — $10k for their newborn
🎯
Reaching a goal
James, 40 — wants $500k by 65
Fill in your numbers
$
%
yrs
$
%
Your balance after 20 years
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You put in
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Free money
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One thing to keep in mind
Principal
Contributions
Interest earned
Year-by-year breakdown
Year
Balance
Total invested
Interest earned
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Wait — what is compound interest exactly?
Simple version: you earn interest on your money. Then next year, you earn interest on your money plus the interest you already earned. It keeps stacking. That's it.
This is why people who start saving at 25 end up with way more than people who start at 35 — even if they save the same amount. Time is the secret ingredient.
The math behind it
A = P × (1 + r/n)^(n×t)
A = What you end up with · P = What you start with · r = Yearly return · n = How often it compounds · t = Years
Common questions
Does it really matter how often interest compounds?
A little, but not as much as people think. Monthly vs daily compounding makes maybe a 0.1% difference over 10 years. What matters much more is your rate and how long you leave it.
What return should I use for stocks/ETFs?
The S&P 500 has returned around 10% per year on average historically, or about 7% after inflation. Most financial planners use 6–7% for long-term projections to stay conservative. For a savings account in 2026, 4–5% is realistic.
Should I include inflation?
If you want to know what your money is actually worth in today's prices — yes. Use 2–3% for a conservative estimate. It won't change how much you have, but it shows the real purchasing power.
What's the Rule of 72?
A handy shortcut: divide 72 by your interest rate to find how many years it takes to double your money. At 7%, that's about 10 years. At 10%, about 7 years. Pretty useful for quick mental math.