Design principles
Every calculator here follows the same four principles, which exist to stop the site from quietly drifting into something less honest over time.
- Client-side only. Calculations run in your browser as you type, and your inputs are not sent to a UK Tax Drag server, which is why there is no "loading…" spinner. If you accept analytics cookies, Google Analytics records the pages you visit, including the page address, and some calculators keep your inputs in the page address so that a result can be shared.
- Published rules, no proprietary data. Every rate, threshold and allowance is drawn from a public HMRC, HMT or statutory source, linked at the foot of the calculator. We do not use commercial tax-intelligence feeds or proprietary data vendors.
- Simple, auditable code. The calculator logic is plain, unminified JavaScript, visible in your browser's developer tools, so you can read it without a source map.
- No rounding games. Intermediate calculations are held at full floating-point precision; only the final displayed number is rounded to the nearest pound (or, where relevant, nearest penny on monthly cashflows).
Shared constants · 2026/27
These values are recorded in one shared table of 2026/27 rates and thresholds. The main income tax calculators read it, automated checks compare the site against it before each update, and the values are rechecked after each Budget and at the start of each tax year.
£12,570
Personal Allowance
£50,270
Basic-rate threshold
£125,140
Additional-rate threshold (PA fully tapered)
£100,000
PA taper start (£1 lost per £2 over)
20% / 40% / 45%
rUK income-tax rates
8% / 2%
Employee NI main / upper rate
£12,570
NI primary threshold
£50,270
NI upper earnings limit
£20,000
ISA annual subscription limit
£3,000
CGT annual exempt amount
£500
Dividend allowance
£1,000
Personal savings allowance (basic rate)
£325,000
Inheritance Tax nil-rate band
£175,000
Residence nil-rate band
Where the site describes the Personal Allowance (£12,570) and the higher-rate threshold (£50,270) as frozen, it means frozen until 5 April 2031, as confirmed at Budget 2025. Any change announced at a future Budget will be listed in the changelog and reflected in each affected calculator's review date.
Income tax & take-home
/ tax-calculator.html
Fiscal drag: a 2025/26 vs 2026/27 comparison.
- Bands applied
- rUK: 20% (£12,571–£50,270), 40% (£50,271–£125,140), 45% (above £125,140). Personal Allowance tapered £1 per £2 of income above £100,000, fully withdrawn at £125,140. Scottish bands are not applied — the calculator shows a banner when Scottish rate-payers are flagged.
- NI bands
- 8% on earnings £12,570–£50,270; 2% above £50,270. Employer NI (15% from 6 April 2025, threshold £5,000) is shown separately in the salary-sacrifice view but not deducted from take-home.
- Student loan
- Plan-specific thresholds and 9% rate (6% for Postgraduate). Plan 5 set at £25,000 threshold, 40-year term.
- Fiscal drag
- Calculated as (2026/27 tax at user's salary × 1.03) minus (2025/26 tax at user's salary). The 3% inflation assumption is editable in an advanced view.
- Sources
- HMRC rates and allowances; EIM76101 (PA taper); IFS frozen-thresholds analysis; OBR March 2026 EFO.
National Insurance
Employee NI is modelled as a simple piecewise-linear function with a single main rate (8%) and an upper rate (2%). Class 1A (employer NI on benefits in kind), Class 2 (historical self-employed), Class 3 (voluntary), and Class 4 (self-employed profits) are out of scope for every calculator on the site — they are flagged where relevant but not computed. The calculators cover PAYE employees only.
Salary sacrifice
/ salary-sacrifice-calculator.html
Pension contribution via salary sacrifice vs from take-home.
- Approach
- Calculates income tax, employee NI, and (separately) employer NI on the full salary, then re-runs all three calculations with the sacrificed amount deducted from gross. The difference is the total saving. For the employee-only figure, employer NI is excluded.
- Employer NI pass-through
- The calc assumes the employer keeps their NI saving unless the user opts in. Opting in adds the employer's 15% saving to the net pension contribution.
- Auto-enrolment floor
- Ignored — calculator is for employees considering sacrifice beyond the statutory 5% / 3% auto-enrolment minimums.
- Annual allowance
- £60,000 standard. Taper from £260,000 adjusted income, down to £10,000 at £360,000+. The calc warns above £60k of contribution but does not stop the calculation.
Pension projection
/ pension-calculator.html
Retirement-pot projection with employer match and tax relief.
- Growth model
- Compound annual growth at a user-chosen nominal rate (default 6%), with contributions added at the start of each year. Fees are deducted annually from the pot at the stated AMC/OCF.
- Tax relief
- Basic-rate relief is applied automatically at 25% of the net contribution (equivalent to 20% gross). Higher/additional-rate relief above basic is shown as a separate line but does not flow back into the pot — it is assumed to be reclaimed via Self Assessment and spent or saved elsewhere.
- State Pension
- Added at the user's SPA (66 / 67 / 68 by date of birth) at full new State Pension (£241.30 per week × 52 = £12,547.60/year for 2026/27) unless the user overrides. Triple lock is assumed to continue — a sensitivity toggle is planned.
- Out of scope
- Defined-benefit schemes, GMP/COPE, contracted-out history, pre-2006 A-day protections, lump-sum allowance (LSA £268,275) / lump-sum and death-benefit allowance (LSDBA £1,073,100) interactions.
Compound interest
/ compound-interest-calculator.html
Long-horizon savings growth with nominal and real views.
- Formula
FV = P(1+r)^n + PMT · [((1+r)^n − 1) / r]with r as the effective annual rate, n as years, and monthly contributions converted to annual equivalents.- Real vs nominal
- Real-return view applies Fisher's equation:
(1+nominal) / (1+inflation) − 1. Default inflation 2.5% (BoE 2% target + 0.5% buffer), editable. - Fees
- Deducted from the growth rate, not from the pot, matching how most UK platforms charge.
ISA vs GIA
/ isa-vs-gia-calculator.html
Quantifies the wrapper premium of the ISA over decades.
- ISA side
- Pure tax-free growth. No dividend, interest or CGT applied.
- GIA side
- Annual dividend yield (default 2%) taxed at the user's marginal dividend rate net of £500 allowance. Capital gains taxed at realisation only — the calc assumes buy-and-hold with a single realisation at the end of the period, net of £3,000 AEA.
- Excess reportable income
- Accumulating ETFs held in a GIA: the calc applies the user's dividend tax rate to ERI even though no cash is received, matching HMRC rules.
Dividend tax
/ dividend-calculator.html
Dividend tax layered on top of salary, using 2026/27 rates.
- Rates applied
- 10.75% (basic), 35.75% (higher), 39.35% (additional) — on dividend income above the £500 allowance. The allowance is used, not just deducted from the taxable amount, per HMRC rules.
- Stacking
- Dividends are treated as the top slice of income, falling into whichever band the salary leaves unfilled.
CGT on property
/ cgt-property-calculator.html
Residential gains under post-April-2024 rates.
- Rates applied
- 18% basic-rate, 24% higher-rate (reduced from 28% from 6 April 2024).
- PRR
- Private Residence Relief apportioned over ownership months with the final 9 months always qualifying. Off-plan purchases treated per HMRC TCGA 1992 s.222 / CG64980 guidance.
- Lettings Relief
- Only available where the owner shared occupation with the tenant (Finance Act 2020 restriction). Capped at lower of PRR / gain attributable to letting / £40,000.
- AEA
- £3,000 for 2026/27.
- Out of scope
- Non-resident CGT, mixed-use properties, ATED-related gains, dependent-relative exemption (pre-1988 acquisitions only).
Stamp Duty Land Tax (SDLT)
/ stamp-duty-calculator.html
England & Northern Ireland, post-31 March 2025 thresholds.
- Bands
- 0% to £125k; 2% £125k–£250k; 5% £250k–£925k; 10% £925k–£1.5m; 12% above £1.5m.
- First-time buyer relief
- 0% up to £300k, 5% £300k–£500k, no relief above £500k purchase price.
- Additional-property surcharge
- 5 percentage points added to each band (raised from 3 points in Autumn Budget 2024).
- Out of scope
- Scotland (LBTT), Wales (LTT), mixed-use, corporate purchases, non-resident 2% surcharge interaction with additional-property surcharge.
Mortgage
/ mortgage-calculator.html
Repayment mortgage amortisation with stress tests.
- Formula
- Standard amortising annuity:
PMT = P · r / (1 − (1 + r)^−n)where r is the monthly rate and n is months. Interest-only option provides a P × r line. - Stress test
- User-chosen rate-shock delta applied at the end of the fixed period, re-amortising over remaining term.
- Out of scope
- Offset mortgages, part-and-part, flexible repayments, LTV-tier pricing curves.
Student loan
/ student-loan-calculator.html
Plans 1, 2, 4, 5 and Postgraduate.
- Thresholds 2026/27
- Plan 1 £26,900 · Plan 2 £29,385 · Plan 4 £33,795 · Plan 5 £25,000 · Postgrad £21,000.
- Interest
- The rate is an input, with a default for each plan. GOV.UK gives the current rates as 4.1% on Plans 1, 4 and 5, between 4.1% and 6% on Plan 2 depending on income (RPI plus up to 3%, currently capped at 6%), and 6% on the Postgraduate Loan.
- Term
- Written off at 25 years (Plan 1), 30 years (Plans 2, 4 and Postgrad), 40 years (Plan 5).
FIRE number
/ fire-calculator.html
Financial independence target and time-to-FI.
- Target
- Trinity-Study-derived 4% safe withdrawal rate (Bengen, 1994; refined Cooley, Hubbard & Walz, 1998). User can adjust to 3.5%, 3%, or a custom SWR.
- Real-terms modelling
- All projections in real pounds. Nominal returns are deflated by CPI (user-editable, default 2.5%).
- Scope
- Treats ISA and pension pots as a single drawdown pool. Does not model the pension-age cliff (i.e., cannot access until 57+) — a "bridge pot" toggle is planned.
Inheritance Tax
/ inheritance-tax-calculator.html
Estate-level IHT with NRB, RNRB, gifts, and charity reduction.
- NRB
- £325,000 standard. Unused NRB from a predeceased spouse added (up to 100% of current NRB).
- RNRB
- £175,000, tapered £1 per £2 above £2m estate. Transferable from predeceased spouse.
- Rate
- 40% standard; 36% where ≥10% of the net estate is left to registered charities.
- Gifts
- Gifts made in the 7 years before death (the seven-year rule), with taper relief bands (0–3y: full 40%, 3–4y: 32%, 4–5y: 24%, 5–6y: 16%, 6–7y: 8%). Annual £3,000 exemption, wedding gifts, and small-gift £250 exemption applied if claimed.
- Out of scope
- Trusts (bare / IIP / discretionary), Business Relief, Agricultural Relief, quick-succession relief, double-taxation treaty relief.
Buy-to-let
/ buy-to-let-calculator.html
Section 24 restricted mortgage-interest relief vs limited-company ownership.
- Personal ownership
- Full rent treated as income. Allowable expenses deducted. Mortgage interest given only as a 20% tax reducer (s.24 Finance Act 2015), not as a deduction. This can push the effective marginal tax rate above 40%/45% for highly-leveraged landlords.
- Limited company
- Full mortgage interest deductible as a business expense. Corporation Tax applied at 19% (profits under £50k), 25% (over £250k), with marginal relief in between. Dividends taxed separately at user's dividend rate when withdrawn.
- SDLT
- Additional-property surcharge (5pp) applied. Company purchases also subject to the 5pp surcharge.
Lifetime ISA (LISA)
/ lisa-calculator.html
25% government bonus with property and age-60 withdrawal rules.
- Bonus
- 25% of contributions up to £4,000/year (£1,000 max bonus). Paid monthly to the LISA provider.
- Property cap
- £450,000 maximum purchase price (unchanged since 2017, flagged as a real-terms reduction inside the calculator).
- Withdrawal charge
- 25% charge on any withdrawal that is not for a first home (up to £450k), after age 60, or on terminal-illness diagnosis. The calc shows the net loss vs an equivalent ISA over the same period.
Crypto tax
/ crypto-tax-calculator.html
Section 104 pooling with same-day and 30-day matching.
- Matching rules
- (1) Same-day acquisitions match first; (2) then acquisitions within 30 days; (3) then the Section 104 pool (average cost).
- Staking rewards
- Treated as miscellaneous income at receipt (CRYPTO21200) at market value on the day, with a fresh acquisition cost for CGT on later disposal.
- Airdrops
- Income-taxed at receipt only if received in return for a service or as part of a trade. Otherwise nil cost basis and CGT-only on disposal.
- Rates
- 18% basic / 24% higher for disposals on or after 30 October 2024 (Autumn Budget 2024 alignment with residential rates).
- Out of scope
- DeFi lending/LP token tax treatment (HMRC guidance remains piecemeal); wrapped-token matching; cross-chain bridges.
Options examples and tools
The options section has its own method. Every worked figure on the options pages, and in the options tools (the strategy builder, the Greeks and implied-volatility labs, the planner and the options CGT calculator), is worked from one dated set of market assumptions and one set of cost, rounding and probability conventions, and the figures are checked before each update. The inputs, the models and the teaching conventions are published on how the options worked examples are built.
Review & corrections
Calculators are rechecked at two points in the year, and whenever a reader reports an error.
| Event | Action | When |
|---|---|---|
| Budget | Calculators affected by the announcements are rechecked, changed thresholds are updated, and the change is listed in the changelog. | After each Budget |
| Start of new UK tax year (6 April) | Affected calculators are rechecked against the new year's rates and thresholds, and their review date is updated. | At the start of each tax year |
| Reader-reported error | Checked against the primary source. If confirmed, the calculator is fixed and the correction is listed in the changelog. | Acknowledged within 5 working days; confirmed errors corrected within 21 working days (corrections policy) |
High-risk calculators also have automated test cases checked before each update. Substantive corrections are listed with the date in the changelog.
Sources
The figures on this page were checked against these primary sources on 3 October 2026. Each calculator also lists its own sources at the foot of its page.
- GOV.UK: Income Tax rates and Personal Allowances (bands, Personal Allowance and its taper)
- GOV.UK: Scottish Income Tax (Scottish bands)
- HM Treasury and HMRC: thresholds maintained until 5 April 2031 (the freeze)
- HMRC: Rates and thresholds for employers 2026 to 2027 (National Insurance thresholds, employer rate and secondary threshold)
- GOV.UK: National Insurance rates and categories (employee rates)
- GOV.UK: Tax on dividends (allowance and rates)
- GOV.UK: Capital Gains Tax rates and allowances
- GOV.UK: Individual Savings Accounts and Lifetime ISA
- GOV.UK: Tax on savings interest (Personal Savings Allowance)
- GOV.UK: Stamp Duty Land Tax residential property rates
- GOV.UK: Inheritance Tax (nil-rate band, rates)
- GOV.UK: Pension annual allowance, tapered annual allowance and lump sum allowance
- GOV.UK: The new State Pension, what you’ll get
- GOV.UK: Repaying your student loan, what you pay (thresholds and current interest rates)
- GOV.UK: Corporation Tax rates
Scope & limitations
Every calculator is a model, and every model simplifies. The site is built for the great middle of UK financial life. The core calculators on this page do not model the following. Where the site covers one of these topics elsewhere, it does so at an introductory level; for a decision, use a specialist (a CIOT or ICAEW member, or STEP for trusts and estates).
- Non-domicile status and the remittance basis (retiring from 6 April 2025 under the FIG regime).
- Trusts of all kinds (bare, IIP, discretionary, relevant-property, bereaved-minor's, 18-to-25).
- Business-specific reliefs: Business Asset Disposal Relief, Business Relief, Agricultural Relief, EIS, SEIS, VCTs.
- Cross-border tax residence, double-taxation treaties, split-year rules, overseas workday relief, offshore-trust anti-avoidance.
- Scottish and Welsh devolved income tax bands. Where a calculation differs materially (for example, the Scottish 42% higher rate), the calculator displays a banner and links to the relevant devolved guidance.
- Pre-1988 capital-gains indexation, rebasing options for 1982/1988, taper relief (abolished 2008).
Using this site for a real decision? The calculators are research tools — fine for exploring, for learning, and for sanity-checking your own arithmetic. Before actually executing a tax decision of any size, take the printed PDF output to a Chartered Tax Adviser (CIOT) or a Chartered Financial Planner. They can see the edge cases we can't.
Next scheduled review: after the next Budget, and again at the start of the 2027/28 tax year. The date of the last review is in the byline at the top of the page.