150 free calculators for the stuff nobody teaches you. UK tax, pensions, salary sacrifice, side hustles. No ads, no signup.

Joined January 2026
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The easiest budget to believe is the one where every bill behaves politely. Real months do not queue. They pile up, then ask why your average looked so sensible.
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A budget can look fine on average and still fail in real life. Averages do not care that the car insurance, school trip and broken appliance all picked the same week.
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An emergency fund sounds boring until one month asks for rent, tires and a dental bill at the same time. The number is not three months for everyone. It depends how fragile the month is. boring-math.com/calculators/…
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If a household needs one perfect month just to stay solvent, the budget is not really balanced. It is waiting for the dentist, the tires or one forgotten renewal to vote.
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A $2,200 rent is not a personality test. At $18 an hour, it takes most of the month before tax before food, insurance, transport or debt enter the room. Telling people to budget harder after that is mostly theatre.
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Student loan interest gets the headline, but the repayment threshold is where graduates feel it month to month. A balance can look absurd and still behave more like an extra tax than normal debt. Run the take-home version before panicking at the headline number: boring-math.com/calculators/…
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The most expensive subscription is usually the one you stopped noticing. £14.99 a month feels harmless because it never becomes a decision again. Five of those is nearly £900 a year before you buy anything new.
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Overpaying £100 a month on a mortgage sounds small until you price it against the interest rate. At 5%, the saving is not just £1,200 a year. It is less interest charged every month after that too. Run your own numbers: boring-math.com/calculators/…
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A £5,000 raise is not £5,000 of new life. Tax, commuting, childcare, debt payments, and one nicer habit all get a vote before your bank balance does.
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Mortgage overpayments sound dull because they are. That is the appeal. A small extra payment can cut years of interest without needing a clever trade or a landlord spreadsheet. boring-math.com/calculators/…
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The most dangerous monthly bill is not the biggest one. It is the one you stopped checking. £11.99 here, £8.99 there, an annual renewal you forgot, a free trial you never cancelled. The spreadsheet does not care that each one felt too small to matter.
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A £5,000 raise is not £5,000 you can spend. Tax, NI, pension, student loan, commuting, childcare, and one lifestyle upgrade all take bites before your bank account sees it. Run the raise as monthly cashflow, not headline salary: boring-math.com/calculators/…
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The dangerous subscription is not the £9.99 one. It is the £9.99 one you stopped noticing, multiplied by six apps, two annual renewals, a phone upgrade, and a gym you keep because cancelling feels like admitting defeat.
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A £5,000 raise is not £5,000 in your bank account. After tax, NI, pension, student loan, and the new monthly bill you quietly accepted, the useful question is smaller: what actually survives? Run the raise before you spend it: boring-math.com/calculators/…
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A raise and a smaller recurring bill hit the same monthly budget from opposite sides. A $75/month bill you cancel is $900/year after tax. To keep $900 from a raise, you may need more than $1,100 of gross pay.
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A bill can be rare and still be normal. That is the part emergency funds struggle with. The expense does not need to happen every month to wreck the month it lands in.
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