Méthodologie

How every figure is sourced, computed, and kept current.

No black boxes. Every calculator on this site uses a documented formula, a published official rate, and a clear update cadence. This page is the reference.

Data sources

All tax bands, thresholds, and rates are pulled directly from the official publications below. We do not use third-party data aggregators, scraped data, or AI-generated approximations.

Source	Scope	URL
gov.uk — Stamp Duty Land Tax	SDLT rates England & Northern Ireland	https://www.gov.uk/stamp-duty-land-tax/residential-property-rates
Revenue Scotland — LBTT	LBTT rates Scotland	https://www.revenue.scot/scottish-taxes/land-and-buildings-transaction-tax
Welsh Revenue Authority — LTT	LTT rates Wales	https://www.wra.gov.wales/land-transaction-tax/
HMRC — Income Tax rates	Income Tax bands England, Wales, NI	https://www.gov.uk/government/publications/rates-and-allowances-income-tax/income-tax-rates-and-allowances-current-tax-year
Revenue Scotland — Income Tax	Scottish Income Tax 6-band	https://www.revenue.scot/scottish-taxes/scottish-income-tax
HMRC — National Insurance	NI Primary Threshold, Class 1 rates	https://www.gov.uk/government/publications/rates-and-allowances-national-insurance-contributions
HMRC — Pension tax relief	Relief at source, annual allowance	https://www.gov.uk/tax-on-your-private-pension/pension-tax-relief
Bank of England — Bank Rate	BoE base rate for mortgage reference	https://www.bankofengland.co.uk/monetary-policy/the-bank-rate

Calculation formulas

Stamp Duty (SDLT/LBTT/LTT)

Progressive band structure: for price P and bands (b₁, r₁), …, tax = Σ of min(P, bᵢ₊₁) − bᵢ × rᵢ (clamped at 0). First-time buyer relief narrows bands; additional-property surcharge adds 3-6% to each rate. Three regions have distinct band structures.

Mortgage monthly payment

M = P × r(1+r)ⁿ / ((1+r)ⁿ − 1), where P = principal,r = monthly rate, n = months. Monthly compounding.

Income Tax

Progressive bands with Personal Allowance taper above £100,000 (reduced £1 per £2 over). Scottish Income Tax uses 6-band structure. NI Class 1 at 8%/2%.

Pension future value

FV = PV(1+r)ⁿ + PMT × ((1+r)ⁿ − 1) / r with monthly compounding.

Update cadence

Tax year runs 6 April to 5 April. We republish all calculator data files within one week of: Autumn Budget, Spring Statement, Scottish Budget, Welsh Draft Budget, and any BoE MPC rate change.

Each calculator page displays its "last updated" date in the footer. If you spot a figure that disagrees with the official source, pleaseContact — we will investigate within one business day.

Limitations

Our calculators model common cases. They do not cover self-employed Class 2/4 NI, capital gains tax, marriage allowance, salary sacrifice, SIPP differences, or Help-to-Buy equity loans. These are flagged as out of scope on each tool's page.

Tous les chiffres sont éducatifs et ne constituent pas un conseil financier. Consultez toujours un professionnel qualifié.