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Verification

How Meridian calculates — shown in full

Every figure below is produced by the same calculation engine that runs live in client meetings — not a simplified stand-in. Each example states its inputs, walks through the arithmetic, and where an external authority publishes an answer of its own (HMRC, DWP, UK statute), shows that figure alongside the engine's own output.

Last checked against the production engine: 18 September 2026
Automated tests
791 passing
Run on every change to the calculation engine, before it reaches a client plan.
External ground truth
HMRC · DWP · statute
UK tax figures are checked against HMRC's own published worked examples, not just our reading of the rules.
Scope
A sample, not everything
These six cover the calculation categories advisers ask about most. The full suite covers far more — see below.

Six worked examples

Real numbers, run through the live engine while this page was written. Where HMRC, DWP or UK statute publish their own answer to the same problem, it's quoted directly from the source.

Core mechanic

Compound growth, no external authority to check against

This is the engine's own arithmetic — there's no HMRC equivalent for "how an investment compounds." Shown so the base mechanic is never a black box either. Deliberately dateless: this is the engine's steady-state annual compounding, not a specific plan's live Year 1 (which prorates to today's date and so is never a fixed number to check).
Opening value £100,000.00 Net assumed growth 6.0% / year Contributions/withdrawals none
01Growth is entered as a single net rate — the adviser's own assumption, already net of any charges they want to model. No hidden fee layer sits underneath it.
02Year 1: £100,000.00 × 1.06 = £106,000.00
03Year 2: £106,000.00 × 1.06 = £112,360.00
04Year 3: £112,360.00 × 1.06 = £119,101.60
Engine output
Year 3 closing value£119,101.60
Reproducible by hand, to the penny
A live plan's actual first year on screen is prorated to the months remaining before it — so it's rarely this clean, and that's expected, not an error. This example uses whole years so the arithmetic above can be checked exactly with a calculator.
Offshore & onshore bonds

Top slicing relief on a chargeable event gain

Source: HMRC Insurance Policyholder Taxation Manual, IPTM3850 "Top slicing relief: examples". HMRC's "Amanda" example, 2022/23 rates.
Employment income £45,000 Bond gain £50,000 Years held 5 Bond type Onshore
01Annual equivalent (the gain "sliced" across the years held): £50,000 ÷ 5 = £10,000
02Liability on the full gain before relief, less the 20% basic-rate credit already deemed paid inside the bond: total liability £8,846
03Liability recalculated on the sliced £10,000, scaled back up, gives the relieved figure of £4,230
04Top slicing relief is the difference: £8,846 − £4,230 = £4,616
Engine vs HMRC published
Relief£4,616.00
Tax payable£4,230.00
Matches HMRC exactly
The engine also handles the harder version of this — multiple chargeable events surrendered in the same tax year, which HMRC assesses together, not separately. That case is verified against HMRC's own multi-event example too.
Pension contributions

Tapered annual allowance for a high earner

Source: HMRC Pensions Tax Manual, PTM057200, "Jon" worked example.
Threshold income £139,100 Adjusted income £178,500 Standard allowance £40,000
01Threshold income is above £110,000 and adjusted income is above £150,000, so both taper gates are breached — the taper applies.
02Excess over the adjusted income limit: £178,500 − £150,000 = £28,500
03Reduction is £1 for every £2 of excess, rounded down to the nearest whole pound: £28,500 ÷ 2 = £14,250
04Tapered allowance: £40,000 − £14,250 = £25,750
Engine vs HMRC published
Tapered annual allowance£25,750
Matches HMRC exactly
This example also pins a rounding case HMRC is explicit about: the reduction rounds down, which can only ever help the client. An earlier version of this rounding logic was found and corrected during testing — the fuzz suite exists precisely to catch this class of error before it reaches a plan.
Estate & IHT planning

Residence nil-rate band taper on a large estate

Source: GOV.UK, "Work out and apply the residence nil rate band for Inheritance Tax". HMRC's own worked example, stated for the 2018/19 tax year — used here to check the taper mechanism, not today's rate. The maximum RNRB is £175,000 in 2026/27.
Estate value £2,100,000 Includes a home worth £450,000 Maximum RNRB (2018/19) £125,000 Taper threshold £2,000,000
01Estate exceeds the £2,000,000 taper threshold by: £2,100,000 − £2,000,000 = £100,000
02RNRB withdraws by £1 for every £2 over the threshold: £100,000 ÷ 2 = £50,000
03Remaining RNRB: £125,000 − £50,000 = £75,000
04Total nil-rate allowance: standard NRB £325,000 + tapered RNRB £75,000 = £400,000
Engine vs GOV.UK published
RNRB taper£50,000.00
Total allowance£400,000.00
Matches GOV.UK exactly
Also checked: a couple carrying both nil-rate bands and both residence nil-rate bands, unused, can shelter up to £1,000,000 — the figure most advisers quote from memory. The engine reproduces it exactly.
Capital gains

A gain that straddles the basic and higher CGT rate

Source: Taxation of Chargeable Gains Act 1992, s1I (as amended), 2026/27 thresholds.
Other taxable income £45,000 Capital gain £20,000 Annual exempt amount £3,000
01Chargeable gain after the annual exemption: £20,000 − £3,000 = £17,000
02Basic rate band remaining before income tips into higher rate: £50,270 − £45,000 = £5,270
03That portion at 18%: £5,270 × 18% = £948.60
04Remainder at 24%: £11,730 × 24% = £2,815.20
Engine output
Total CGT due£3,763.80
Matches published arithmetic
The engine also models a genuine planning lever here: a gross pension contribution extends the basic-rate band, which pulls more of the gain into the 18% band — a 6-point saving on the amount shifted. That's checked as its own test, not left to emerge by accident.
Retirement income

UK State Pension rate and age

Source: DWP, "Benefit and pension rates 2026/2027", GOV.UK.
Full new State Pension, weekly £241.30 Triple lock rise from 2025/26 4.8%
012025/26 weekly rate £230.25, uprated 4.8% under the triple lock: £230.25 × 1.048 = £241.30
02Annualised over 52 weeks: £241.30 × 52 = £12,547.60
03State Pension age is read from the client's date of birth against the legislated cohort timetable (Pensions Acts 2007 & 2014) — 66, a fractional transitional age, 67, or 68 depending on when they were born.
Engine vs DWP published
Weekly£241.30
Annual£12,547.60
Matches DWP exactly

What this page is, and isn't

These six examples are a sample chosen to span the categories advisers ask about most — they can't model every scenario a real plan produces, and they're not a substitute for reviewing a specific client's output. What they do show honestly: the engine isn't privately-held arithmetic taken on trust. Where an external authority publishes a worked answer, we reproduce it exactly, and you can check the working by hand above.

For compliance and audit teams

If you're evaluating Meridian as a vendor, we can send a fuller methodology pack covering the full test suite, calculation sources for every UK figure, and how the engine is verified on every release — written for a compliance review, not a sales page.

Request the methodology pack Book a demo instead