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. Your inputs never leave your browser. Calculations run as you type. There is no server, no logging, no analytics pixel. This is why there is no "loading…" spinner: there is nothing to load.
- 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. Every calc is <400 lines of plain JavaScript, visible in your browser's View Source. There is no build step and no minification, so you can read the logic 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 hard-coded across all calculators that use them. They are reviewed within 48 hours of any fiscal event and on 6 April each 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
Thresholds shown as "frozen" on the site are those confirmed frozen through to 5 April 2028 under the Spring Budget 2021 / Autumn Statement 2022 measures. Any future change announced at a future fiscal event will appear on the forthcoming site changelog and inside each affected calculator's "Last reviewed" line.
Income tax & take-home
/ tax-calculator.html
The fiscal-drag engine: 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 Personal Allowance tapered £1 per £2 of income above £100,000, fully withdrawn at £125,140.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 (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 (£230.25 per week × 52 = £11,973/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
- 8.75% (basic), 33.75% (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 £24,990 · Plan 2 £27,295 · Plan 4 £31,395 · Plan 5 £25,000 · Postgrad £21,000.
- Interest
- Plan 2: RPI + 0–3% banded by income (capped at prevailing market rate under SLC's "prevailing market rate" cap since 1 Sep 2022). Plans 1, 4, 5: RPI only. Postgrad: RPI + 3%.
- Term
- Written off at 25 years (Plans 1, 2, 4), 30 years (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
- 7-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 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 penalty
- 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.
Review & corrections
The site follows a two-cadence review schedule.
| Event | Action | Turnaround |
|---|---|---|
| Budget / Spring Statement / Autumn Statement | Every calculator re-checked against announcements. Changed thresholds updated. A "changelog" note added to any modified calc. | ≤ 48 hours |
| Start of new UK tax year (6 April) | Full top-to-bottom recheck. Every threshold, every rate, every linked source. "Last reviewed" date updated even where nothing has changed. | Complete by 13 April |
| HMRC manual update (caught by RSS feeds we monitor) | Affected calculator flagged for review. Update typically within 7 days. | ≤ 7 days |
| Reader-reported error | Acknowledged inside 48 hours. If confirmed, fixed and a correction note added to the page. | ≤ 48 h triage |
Corrections are logged at the bottom of each affected page with the date and a short description of what changed. The site does not silently re-edit numbers once published. A full site-wide changelog is on the roadmap.
Scope & limitations
Every calculator is a model, and every model simplifies. The site is built for the great middle of UK financial life. The following are deliberately out of scope site-wide:
- 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 (10%), 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 (e.g., Scottish 42% intermediate 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.
Last reviewed 18 April 2026. Next scheduled review: 6 April 2027, or earlier if a fiscal event intervenes.