Metodología

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, pleaseContacto — 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.

Todas las cifras son educativas y no constituyen asesoramiento financiero. Consulte siempre a un profesional cualificado.