Guides
Plain-English explainers on the questions our calculators answer. Each guide ends with the relevant tool, so you can run the numbers on your own situation.
Burn rate and runway explained
Gross vs net burn, how to calculate months of runway, what counts as a safe buffer, default-alive vs default-dead, and how to extend it.
StartupsUnit economics explained
Contribution margin, CAC, LTV, the LTV:CAC ratio and CAC payback — how to tell if each sale actually makes money before you scale.
Small businessHow UK Corporation Tax works (small companies)
The 19% small profits rate, the 25% main rate, marginal relief in the £50k–£250k band, the associated-companies trap, and when to pay — with a free calculator.
Saving & investingWhat inflation really does to your money
How purchasing power erodes, the rule of 72, real vs nominal returns, and why cash held too long quietly loses value.
MarketingWhat is a good ROAS?
Why a "good" ROAS depends entirely on your margin — break-even ROAS, ROAS vs ROI, and the mistakes that flatter the number.
US MortgagesHow much house can I afford? The 28/36 rule (US)
The US affordability test in plain English — the 28/36 rule, front-end and back-end DTI, PITI and PMI — and why your other debts quietly shrink your budget.
US MortgagesHow US property tax changes your payment — by state
Property tax can add $100–$800 a month to the same house. How PITI and escrow work, which states cost most, and a calculator with presets for all 50 states.
Stamp DutyHow does UK stamp duty work?
Rates, bands, first-time buyer relief and the 5% additional-property surcharge — with worked examples and a free calculator.
Buy-to-letWhat is a good rental yield?
Gross vs net yield, what counts as good in the UK, and why cashflow and cash-on-cash ROI matter more than the headline number.
Saving & investingHow compound interest works
The formula, the rule of 72, and why starting ten years earlier can beat saving three times as much later.
Salary & taxUK take-home pay explained: tax, NI and what you keep
The 2025/26 income tax bands, National Insurance, the personal allowance and the £100k trap — what's really deducted from your salary, with a worked example.
MortgagesHow much mortgage can I really afford in 2026?
Lenders quote a multiple of your income — but what you can actually live with depends on rate, term, and what's left after the rest of life.
Stamp DutyHow does stamp duty work for second homes?
The 5% surcharge, the 36-month rule, and the trap people fall into when they buy before selling.
FIREWhat is FIRE — and can I really retire early?
The 25× rule, the 4% rule, and how a small change in savings rate moves your finish line by a decade.
Side HustleIs my side hustle actually profitable?
Most side hustles look profitable until you cost in your own time. Here's how to tell whether yours pays better than a Saturday shift.
PropertyRent vs Buy: when does buying actually win?
"Rent is dead money" is a myth. The real answer is the breakeven horizon — and why staying under 5 years usually means renting wins.
InvestingCompound interest: 25 vs 35 changes everything
A decade of delay can more than halve your final pot. The maths is simple — but the consequences are extreme.