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Free finance calculators that do the boring math properly
Free finance and trading calculators. The simple money maths nobody taught you. One page per tool. Formula, worked example, FAQ. No signup, no market data feeds, no fluff.
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Percentage change
From A to B, what percent did it move? Also works backwards.
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Interest
Simple or compound. Principal, rate, time, how often it compounds.
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Rule of 72
Years to double ≈ 72 ÷ rate. We also show the exact answer.
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ROI
Profit over capital. Optional annualised figure if you held it for years.
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CAGR
The smoothed yearly rate that gets you from A to B.
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Present value
What is money later worth in money now? Lump sum or annuity.
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Purchasing power
What inflation does to your money. Real value, percent lost, years to half.
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Margin
Cost, price, margin, markup. Stop mixing them up.
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APR / loan
Payment, total interest, EAR. Optional fees. Year-by-year view.
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Mortgage
Payment, SDLT, cash upfront, real terms, house vs S&P/Treasuries.
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Odds converter
Fractional, decimal, American, implied probability. Spot the overround.
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Expected value
Your edge in pounds and percent. Break-even probability included.
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Arbitrage betting
Is it a sure bet? Stakes, guaranteed profit and what rounding costs you.
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Pip value
Pip value and P&L for N pips. You supply conversion rates.
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Kelly criterion
How much to stake when you think you have an edge. Fractional Kelly included.
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Futures size
Entry, stop, max loss: how many contracts to buy or sell.
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