Our calculation methodology

Scope and editorial responsibility

The MyUKTools Team maintains this independently operated website. Each calculator implements a defined model, not every circumstance covered by UK law or a lender or payroll system. Content and worked examples were checked on 31 October 2026.

Rate-dependent pages link to official guidance. We compare published thresholds and examples with the calculation code before updating a review date. A review date records that check, not a guarantee that future changes are already incorporated. Report an error with example inputs, expected and actual outputs, and the relevant source.

Salary: annual estimates for 2026/27

The Salary Calculator subtracts pension contributions (the entered percentage of full gross salary) before estimating Income Tax. The standard Personal Allowance is £12,570, reduced by £1 for each £2 of modelled income above £100,000. The taxable basic-rate band is £37,700; higher and additional rates are applied progressively. England, Wales and Northern Ireland are supported; Scotland is disabled.

Employee NI uses annual gross income: 8% between £12,570 and £50,270, then 2% above. One selected student-loan plan uses its annual threshold and rate against gross income; simultaneous undergraduate and postgraduate loans are not combined. Pensions do not reduce NI or loan deductions in this model. Salary sacrifice, relief-at-source pensions, special NI categories, other tax codes, other income and payroll-period rounding are excluded.

Take-home pay is gross salary minus pension, Income Tax, NI and the selected loan. Monthly and weekly amounts divide annual values by 12 and 52; displayed main results round to whole pounds. Sources: Income Tax, 2026/27 payroll rates, student loans and pension relief.

Mortgage repayments: monthly amortisation

The Mortgage Repayment Calculator sets the loan to property price minus deposit. It rounds years × 12 to a whole number of monthly payments. With loan P, monthly interest rate r (annual percentage ÷ 1,200) and payment count n, payment = P × r ÷ (1 − (1 + r) raised to −n). At zero interest it uses P ÷ n.

Total repayments use the unrounded monthly payment multiplied by n; total interest subtracts P. Money outputs then round to pennies, although some result cards display whole pounds. Multiplying the displayed rounded payment can therefore differ slightly from the total. The borrowing rate is held constant for the whole term, with no fees, daily interest, rate resets or interest-only period. APRC is not the input rate. See MoneyHelper on rates and costs.

Mortgage overpayments: balance simulation

The Mortgage Overpayment Calculator first calculates the normal monthly repayment from the original balance and remaining term. It compares two monthly simulations: normal payments, and normal payments plus the monthly extra. The entered lump sum, capped at the balance, is applied immediately before the first interest charge.

Each month adds annual rate ÷ 12 interest, then deducts the payment, capped at the amount owed. The normal repayment stays fixed; the term shortens rather than the lender recalculating a lower payment. Internal balances are not rounded each month; the simulation stops below half a penny and has a 1,200-month safety limit. Interest saved compares simulated interest totals, excluding fees, early repayment charges, allowance limits and any return forgone on savings. Read MoneyHelper on overpayment trade-offs.

Stamp Duty: marginal residential bands

The Stamp Duty Calculator applies each selected SDLT rate only to the portion of price in that band and sums the tax. It covers straightforward residential purchases in England and Northern Ireland, using standard bands from 1 April 2025. First-time buyer relief uses its separate bands only through £500,000; above that price the whole purchase uses standard bands.

Additional-property mode applies the higher bands without determining eligibility. It is unsuitable below £40,000 and does not assess main-residence exceptions, refunds, non-UK-resident surcharges, companies, lease rent, mixed-use property or special reliefs. The effective rate is total modelled tax ÷ price × 100. Money is displayed to pennies. Confirm eligibility with the residential rates and higher-rate guidance.

VAT: one amount at one rate

For rate r expressed as a decimal, the VAT Calculator adds VAT as net × r and gross as net × (1 + r). Removing VAT divides gross by (1 + r); VAT is gross minus the resulting net amount. Each output is rounded to pennies after the calculation.

The interface offers 20%, 5% and 0%. It assumes the chosen treatment is correct and does not determine VAT registration, exemption or the supply category. Mixed-rate items must be calculated separately. It does not reproduce every invoice-line rounding method, special scheme or VAT return. Check HMRC VAT rates; zero-rated and exempt supplies are different.

Pay rises: gross salary comparisons

The Pay Rise Calculator uses a positive entered new salary in preference to a percentage. Otherwise new salary = current salary × (1 + percentage ÷ 100). Annual difference = new minus current; percentage change = difference ÷ current × 100. Monthly, weekly and daily equivalents divide annual amounts by 12, 52 and 260.

The 260-day divisor is a five-day-week comparison, not actual days worked or a contractual daily rate. It includes no tax, deductions, bonuses, inflation or change in weekly hours. Outputs display pennies without rounding the intermediate calculation. For after-tax comparisons use the Salary Calculator with each salary and the same supported assumptions.

Working hours: clock times and repeated shifts

The Working Hours Calculator converts clock times to minutes. If finish is earlier than start it adds 1,440 minutes to finish, representing one overnight shift. It subtracts the entered break, then multiplies the daily minutes by days per week. Decimal hours are minutes ÷ 60; 45 minutes is 0.75 hours, not 0.45.

The same shift and break repeat every day. Identical start and finish are invalid; full-day shifts, dates, time zones and daylight-saving changes are not handled. This arithmetic does not establish paid-break rights, overtime pay or legal working-time compliance. Consult rest-break guidance and weekly-hours rules.

Holiday: regular working days for a full leave year

The Holiday Entitlement Calculator uses the smaller of days per week × 5.6 and 28 days. Total entitlement is the larger of that statutory minimum and the entered full contractual allowance. Bookable days subtract only the bank holidays entered as included; the tool rejects an included-bank-holiday figure larger than total entitlement.

Fractional days are retained in the calculation. Do not round regular-hours statutory leave down. An hours-based calculation is more suitable when working days differ in length. This model does not calculate holiday pay, irregular-hours accrual, part-year work, part-year joining/leaving or carry-over. See statutory entitlement, the official calculator and Northern Ireland guidance.

Checking and using an estimate

Worked examples are checked against the existing calculation engines. Regression checks exercise all eight interfaces on desktop and mobile, with indexing and consent checks kept separate from numeric results. These checks help catch regressions; they do not certify a tool for every transaction, employment arrangement or future rule change.

Use fictional or rounded inputs when reporting an error. For an important decision, check the relevant official guidance and a lender, employer, HMRC or suitably qualified adviser as appropriate. No calculator result is personalised financial, tax, legal or employment advice.