How we check Palarid’s calculations
This page covers the money maths, not all 134 tools. The heading used to promise that every number was checked, which is more than this page delivers: 44 known-answer checks cannot speak for a product this size, and in September 2026 two of them were quietly passing on last year’s Scottish tax bands because the runner held its own copy of the band table and agreed with itself. Both things are fixed — the runner now computes with the same engine the public calculators use, and every expected value below is worked by hand from the published government tables, with the arithmetic written out so you can follow it without trusting our code. What the wider suite covers is listed underneath. Below is every known-answer check we run against Palarid's money maths — the expected value, the value our formulas computed, and where the expected value comes from.
These checks run in every release check. Last run: 29 September 2026 (Palarid v4.94.0) · Figures for the 2026/27 tax year
node verify.js.
Income tax & NI
| Check | Expected | Computed | |
|---|---|---|---|
| £20,000 salary — income tax HMRC bands 2026/27 | £1,486.00 | £1,486.00 | PASS |
| £20,000 salary — National Insurance 8% between £12,570–£50,270 | £594.40 | £594.40 | PASS |
| £50,270 (top of basic) — income tax 20% × £37,700 | £7,540.00 | £7,540.00 | PASS |
| £60,000 — take-home worked example on /t/take-home-pay-calculator/ | £45,357.40 | £45,357.40 | PASS |
| £125,140 — allowance fully tapered, tax £1 per £2 taper above £100k | £42,516.00 | £42,516.00 | PASS |
| £150,000 — income tax additional rate 45% | £53,703.00 | £53,703.00 | PASS |
Scottish income tax
| Check | Expected | Computed | |
|---|---|---|---|
| £60,000 — Scottish income tax 3,967×19% + 12,989×20% + 14,136×21% + 16,338×42% = 753.73 + 2,597.80 + 2,968.56 + 6,861.96 | £13,182.05 | £13,182.05 | PASS |
| £33,493 — Scotland equals England (Scotland side) the crossover: the 19% starter band saves £39.67, the 21% band costs 1% above £29,526 | £4,184.60 | £4,184.60 | PASS |
| £33,493 — Scotland equals England (England side) (33,493 − 12,570) × 20% — the same bill both sides of the border | £4,184.60 | £4,184.60 | PASS |
Pension
| Check | Expected | Computed | |
|---|---|---|---|
| £20,000 pot + £300/mo, 0% return, 37 years 0% must equal the sum of deposits exactly | £153,200.00 | £153,200.00 | PASS |
| £300,000 drawdown, 0%, 300 months even draw when growth is zero | £1,000.00 | £1,000.00 | PASS |
Mortgage
| Check | Expected | Computed | |
|---|---|---|---|
| £250,000 @ 7% over 30 years — monthly standard amortisation formula | £1,663.26 | £1,663.26 | PASS |
Debt honesty
| Check | Expected | Computed | |
|---|---|---|---|
| £5,000 @ 29.9% APR, minimums only — must report NEVER, not a date minimum payments cannot cover the interest | 0 | 0 | PASS |
| same debt with £150/month extra — clears in 36 months what actually changes the outcome | 36 | 36 | PASS |
Student loans
| Check | Expected | Computed | |
|---|---|---|---|
| £35,000 on Plan 2 — annual repayment 9% above £29,385 | £505.35 | £505.35 | PASS |
| £45,000, Plan 2 + Postgraduate combined the two deductions stack — 15% combined marginal | £2,845.35 | £2,845.35 | PASS |
Salary sacrifice
| Check | Expected | Computed | |
|---|---|---|---|
| £45,000 salary, £3,000 sacrifice — take-home falls by only £3,000 into the pension; £600 tax + £240 NI not charged | £2,160.00 | £2,160.00 | PASS |
Boundaries · income tax
| Check | Expected | Computed | |
|---|---|---|---|
| £0 — income tax nothing to tax | £0.00 | £0.00 | PASS |
| negative input — income tax invalid input must not produce a figure | £0.00 | £0.00 | PASS |
| £12,569 (allowance − £1) below the £12,570 personal allowance | £0.00 | £0.00 | PASS |
| £12,570 (allowance exactly) the allowance itself is tax-free | £0.00 | £0.00 | PASS |
| £12,571 (allowance + £1) £1 × 20% | £0.20 | £0.20 | PASS |
| £12,570.50 (decimal input) £0.50 × 20% | £0.10 | £0.10 | PASS |
| £50,271 (basic limit + £1) £7,540 + £1 × 40% | £7,540.40 | £7,540.40 | PASS |
| £100,000 (taper starts above) £7,540 + (100,000 − 50,270) × 40% = 7,540 + 19,892 | £27,432.00 | £27,432.00 | PASS |
| £100,002 (taper: £1 of allowance lost) £2 more income at 40% (0.80) + £1 of allowance lost at 40% (0.40) | £27,433.20 | £27,433.20 | PASS |
| £125,141 (allowance gone + £1) £42,516 + £1 × 45% | £42,516.45 | £42,516.45 | PASS |
| £1,000,000 (large input) £42,516 + (1,000,000 − 125,140) × 45% = 42,516 + 393,687 | £436,203.00 | £436,203.00 | PASS |
Boundaries · National Insurance
| Check | Expected | Computed | |
|---|---|---|---|
| £12,570 — NI primary threshold | £0.00 | £0.00 | PASS |
| £12,571 — NI £1 × 8% | £0.08 | £0.08 | PASS |
| £50,270 — NI £37,700 × 8% | £3,016.00 | £3,016.00 | PASS |
| £50,271 — NI £3,016 + £1 × 2% | £3,016.02 | £3,016.02 | PASS |
Boundaries · Scottish income tax
| Check | Expected | Computed | |
|---|---|---|---|
| £16,537 (top of starter band) 3,967 × 19% | £753.73 | £753.73 | PASS |
| £29,526 (top of basic band) 753.73 + 12,989 × 20% | £3,351.53 | £3,351.53 | PASS |
| £43,662 (top of intermediate band) 3,351.53 + 14,136 × 21% | £6,320.09 | £6,320.09 | PASS |
| £43,663 (higher rate + £1) 6,320.09 + £1 × 42% | £6,320.51 | £6,320.51 | PASS |
Boundaries · student loans
| Check | Expected | Computed | |
|---|---|---|---|
| £29,385 on Plan 2 (threshold) nothing at the threshold | £0.00 | £0.00 | PASS |
| £29,386 on Plan 2 (threshold + £1) £1 × 9% | £0.09 | £0.09 | PASS |
| £21,000 Postgraduate (threshold) nothing at the threshold | £0.00 | £0.00 | PASS |
| £21,001 Postgraduate (threshold + £1) £1 × 6% | £0.06 | £0.06 | PASS |
Boundaries · growth and borrowing
| Check | Expected | Computed | |
|---|---|---|---|
| £10,000 at 5% for 10 years, monthly compounding 10,000 × (1 + 0.05/12)^120 (independent 40-digit calculation) | £16,470.09 | £16,470.09 | PASS |
| £200 a month at 4% for 25 years 200 × ((1 + r)^300 − 1) / r, r = 0.04/12 (independent) | £102,825.91 | £102,825.91 | PASS |
| £200,000 mortgage at 4.5% over 25 years P·r / (1 − (1 + r)^−300) (independent) | £1,111.66 | £1,111.66 | PASS |
| £250,000 mortgage at 0% over 30 years 250,000 ÷ 360 — a zero rate must not break the formula | £694.44 | £694.44 | PASS |
What this does and does not prove
Being straight with you about the limits. These checks verify the formulas — the band logic, thresholds and edge cases — against externally known answers. They do not exercise every button in every one of Palarid’s 134 tools — separate release tests open and use each tool in a real browser, and they cannot know your personal tax code, benefits in kind or other income. An estimate is an estimate; your payslip and HMRC are the authoritative record.
- Where the expected values come from: HMRC published rates and thresholds for 2026/27, the standard amortisation and annuity formulas, and hand-worked examples published openly on the relevant tool pages so you can re-derive them yourself.
- Why the 0% cases matter: several calculators here once rendered
NaNwhen given a 0% rate, because the textbook formula divides by zero there. We fixed them and now test exactly those inputs every release. - Why the "Never clears" case matters most: a debt tool that invents a payoff date for an unpayable debt is worse than no tool. Ours says so, and we test that it says so.
- Found a number we got wrong? Tell us. Corrections to this page are treated as the highest-priority work in the project — and as the privacy policy shows, we publish corrections rather than quietly editing them.
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