UK tools that actually get the maths right.
A growing collection of calculators and lookups for the UK — tax, property, household, and the garden. Built against current HMRC, ONS, and government data, with the logic open and unit-tested.
In the works
Each tool ships as its own page and is kept current when rates or thresholds change.
Take-home pay calculator
Income tax, National Insurance, all student loan plan types.
PlannedStamp duty calculator
SDLT for purchases, second homes, first-time buyers — kept current.
PlannedMortgage overpayment calculator
Term reduction and interest saved, with overpayment penalty notes.
PlannedPension & tax-relief calculator
Relief at source vs net-pay, annual allowance taper for higher earners.
PlannedCouncil tax band lookup
By postcode, with charges for the relevant band and authority.
PlannedEPC running-cost estimator
Band → estimated £/year, with improvement suggestions.
PlannedAllotment sowing calendar
Sow/harvest windows by region using actual frost-date data.
Planned
Why wikt.uk?
Most UK calculator results in search are stale, wrong on edge cases, or quietly US-centric. Allowances haven’t been updated, NI tables are last year’s, student loan plan types are lumped together, and the “UK” default currency is often dollars.
Wikt is the fix. Each calculator’s logic is a small, plain TypeScript module with unit tests you can read. When a rate changes, the data file is updated and the tests catch any drift. No black boxes.