Everyday money math

Finance

Calculators for the numbers that quietly run your financial life — what your money does while it sits, what a loan actually costs over time, and how far off financial independence is.

Student Loan Calculator

UK Plans 1, 2, 4, 5 and postgraduate, projected across a whole career — what you actually repay, and whether you ever clear it.

9% above threshold · written off after 25–40 years
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Inflation Calculator

What a price in any past year is worth in today’s money — and what today’s money will be worth later, if you say what you assume.

amount × index(to) ÷ index(from)
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Compound Interest Calculator

Starting amount, regular contributions, rate, and time — watch the growth curve, and see the Rule of 72 checked against the exact formula.

A = P(1 + r⁄n)ⁿᵗ
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Mortgage Calculator

Home price, down payment, rate, and term — monthly payment, full amortization schedule, and how much an extra payment really saves.

M = P·r(1+r)ⁿ ⁄ [(1+r)ⁿ−1]
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Car Finance Calculator

UK hire purchase & PCP, US auto loans — deposit, balloon, trade-in, fees, term compare, and a full payment schedule.

loan · HP · PCP · UK & US
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Currency Converter

ECB reference rates via Frankfurter — convert between USD, EUR, GBP and 20+ currencies. Same rates as Unit Converter’s Currency category.

ECB · Frankfurter · mid-market
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Salary Converter

Convert pay between hourly, daily, weekly, monthly and annual — and compare it to the UK and US minimum wage.

gross · UK & US
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Tip Calculator & Bill Splitter

Regional tipping norms, correct tip-on-pre-tax handling, and fair splitting when everyone ordered something different.

tip · split · regional norms
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FIRE Calculator

Your FIRE number from spending and safe withdrawal rate, years to reach it, and your Coast FIRE number.

spending ÷ withdrawal rate
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Debt Payoff Calculator

Snowball vs. avalanche compared side by side — payoff time, total interest, and a real month-by-month simulation.

avalanche minimises interest
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Rent vs Buy Calculator

Net cost of buying vs. renting and investing the difference — not just monthly payment against rent.

opportunity-cost model
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Important Not financial advice. Every figure here is an illustrative estimate for general information and education. It is not financial, investment, tax, mortgage or legal advice, not a personal recommendation, and not a quote or an offer. Rules of Thumb is not authorised or regulated by the Financial Conduct Authority and does not carry out regulated activities. Rates, fees and thresholds change and may be out of date. Before acting on anything here, speak to a qualified financial adviser, mortgage broker, accountant or your lender, who can take your own circumstances into account. See the Terms of Use.
Results are for reference only. Nothing here is financial advice — verify any numbers you rely on with a bank, advisor, or independent calculator.