Guides · Allowances, deductions, credits

Allowances vs deductions vs credits

Three things that lower your tax

Whatever the country, there are only three ways to lower a tax bill:

1. Shield some of your income from tax — UK calls this an allowance. The US calls the same thing a deduction when it is a fixed dollar amount (the standard deduction) and an exemption when it is tied to a specific category (a personal exemption, historically).
2. Subtract spending from your taxable base — both countries call this a deduction in the technical sense: self-employment expenses, certain retirement contributions, and so on.
3. Subtract money directly from the tax bill — both countries call this a credit. A £200 credit saves £200 of tax; a £200 deduction at a 20% marginal rate only saves £40 of tax.

The vocabulary overlaps and shifts. The math does not.

Allowance — shield income

An allowance is a slice of income the government agrees not to tax. The UK's Personal Allowance of £12,570 (2026/27) is the textbook example. The first £12,570 of employment income is taxed at 0%.

On the US side, the closest analogue is the standard deduction ($15,750 for a single filer in tax year 2026, per Rev. Proc. 2025-32). It does the same job — shields income from tax — but the US calls it a deduction because it is subtracted from gross income before the brackets run.

Some allowances taper. The UK Personal Allowance shrinks by £1 for every £2 of adjusted net income above £100,000, reaching £0 by £125,140. TaxMetria's UK calculator does not model this taper in v1; it is a known limitation, not a bug. See the assumptions page for the full list.

Deduction — shrink the base

A deduction is an amount you subtract from your gross income to arrive at the base the brackets run against. The two flavors:

• Standard deduction — a flat amount everyone in a filing class gets. Single filer, married filing jointly, head of household. You take it without proving anything.
• Itemized deductions — specific categories you add up and subtract instead of the standard amount, if they exceed it. Mortgage interest, state and local taxes (capped at $10,000), charitable contributions, certain medical expenses above an AGI threshold.

In the UK, the equivalent of "itemizing" is rare because most employment income goes through PAYE and most allowances are universal. Self-employed taxpayers can deduct legitimate business expenses, but those are conceptually closer to cost-of-earning than to the US itemized-deduction bucket.

TaxMetria's US calculator uses the standard deduction and does not model itemizing. That is a conscious scope cut for v1 — see the methodology page.

Credit — knock off the bill

A tax credit reduces your tax bill dollar-for-dollar (or pound-for-pound). A £200 credit at a 20% marginal rate is worth £200 of tax saved; a £200 deduction at the same rate is worth only £40.

Some credits are refundable: if your bill is £100 and the credit is £200, the government cuts you a cheque for £100. Others are non-refundable: they reduce your bill to zero and the rest is forfeit.

Common credits:

• US: Child Tax Credit, Earned Income Tax Credit (refundable), Saver's Credit, American Opportunity Credit (partially refundable).
• UK: the term is rarely used because most UK tax reliefs are structured as allowances or zero-rated bands. The closest equivalent is a tax reduction in HMRC terminology — for example, the Marriage Allowance transfer, which directly reduces a couple's combined bill rather than their taxable income.

TaxMetria's v1 calculators do not model any tax credits on either side. Credits are highly personal (dependents, education, retirement contributions) and out of scope for the single-filer baseline the calculator ships with.

Why the difference matters

Deductions are worth more to high earners than to low earners, because they are applied to income that would have been taxed at higher rates. Credits are worth the same flat amount to everyone, regardless of bracket.

Concrete example: a $1,000 deduction is worth $220 to a US taxpayer in the 22% bracket, $320 to one in the 32% bracket, and $370 at the top. A $1,000 credit is worth $1,000 to either of them.

This is why refundable credits are the more powerful anti-poverty tool, and why deductions are the more powerful "tax planning" tool for high earners.

US vs UK vocabulary at a glance

What TaxMetria models

The US calculator:

• Standard deduction (single filer, no dependents)
• Personal exemption — none (suspended through 2025 and not reintroduced for tax year 2026 in Rev. Proc. 2025-32)
• No itemized deductions
• No tax credits
• No state tax

The UK calculator:

• Personal Allowance of £12,570 (no taper modeled — see assumptions)
• No Marriage Allowance transfer
• No Blind Person's Allowance
• No tax reductions or credits
• Scottish rates not modeled (only England / Wales / Northern Ireland bands)

Each exclusion is deliberate — the calculator ships a clean single-filer baseline so the math is auditable. Adding more scenarios is a Batch 3+ decision, not a v1 decision.

Related

• How progressive income tax works — the band walk
• Marginal vs effective tax rate
• Methodology — engine, data, and tests
• Assumptions — every scenario we model and every one we don't
• Sources — primary government references for every number