Gross-up

Gross-up is the payroll calculation that inflates a gross amount so the net delivered to the employee equals a guaranteed figure.

For payroll and mobility teams, the real question isn't whether to gross up. It's how much the calculation actually adds to the employer cost line once host-country tax, employee social security, and employer-side contributions are all stacked on top.

The base mechanic is one formula: gross = net divided by (1 minus the marginal effective rate). It looks simple on a slide and gets messy in payroll because the marginal rate moves with bands, contribution ceilings, and host-country surcharges.

UK payroll teams meet gross-up in three places: tax-equalised mobility, PAYE Settlement Agreements on benefits-in-kind, and sign-on or relocation bonuses written as a net figure. US payroll teams hit it most often on bonuses, where IRS Publication 15-A sets the 22 per cent supplemental withholding rate that anchors the calculation.

How does the gross-up formula actually work?

The clean version is one line: gross equals net divided by (1 minus rate). The complication is the rate, which usually isn't a single number.

The single-rate version

If the entire payment sits inside one tax band and one social-security band, the formula collapses cleanly. A £10,000 net bonus to a UK higher-rate taxpayer (40 per cent income tax plus 2 per cent employee NI) grosses up at gross = 10,000 / (1 - 0.42), giving roughly £17,241 before employer NI lands on top.

Iterative gross-up across bands

When the payment straddles bands, the iterative method takes over. Payroll runs the calculation, sees the gross figure pushes part of the payment into the next band, recalculates, and repeats until the net lands on target.

Most modern payroll systems iterate automatically. Manual gross-up by hand still happens on one-off relocation lump sums and PSA returns, where mistakes are easy and only surface at year-end reconciliation.

What the rate actually has to include

A gross-up rate is only useful if it captures every employee-side deduction that sits between gross and net. Skipping any of these understates the gross and leaves the employee short.

• Income tax: applied at marginal, not headline, rate.
• Employee social security: UK NI, US FICA, French CSG/CRDS, German Sozialversicherung.
• Local surcharges: solidarity in Germany, high-income contribution in France.
• State or regional tax: US state withholding, Belgian municipal additional, Italian regional and municipal.
• Pension deductions: if the benefit feeds pensionable pay.

When does payroll actually have to gross up?

Gross-up isn't a default. It fires in specific scenarios where the employer has agreed, explicitly or by policy, to deliver a net figure rather than a gross one.

UK: PSA, PAYE76000 and Class 1B NI

HMRC's PAYE Manual at PAYE76000 sets the rules for a PAYE Settlement Agreement. The employer agrees to pay tax on minor or irregular benefits in a single annual return, calculated at the employee's marginal rate and grossed up.

Class 1B National Insurance then applies at 15 per cent on the grossed-up tax figure, not just the benefit. A £1,000 benefit to a higher-rate employee can land near £700 of additional employer cost once the PSA gross-up and Class 1B NI compound.

US: IRS supplemental rate and the 22 per cent default

IRS Publication 15-A treats bonuses and most one-off payments as supplemental wages. Payroll can use the flat method, applying 22 per cent federal withholding on payments up to one million dollars, or aggregate the payment with regular wages and withhold at the resulting marginal rate.

For a net-quoted sign-on bonus, payroll grosses up using the supplemental rate plus state withholding and FICA. The 22 per cent flat rate makes the formula tidier than the UK iterative version, but state-level additions vary widely.

Mobility: tax-on-tax under equalisation policies

In tax-equalised assignments, the employer pays the assignee's host-country tax directly. That payment is itself a taxable benefit in most countries, which forces a gross-up so the assignee stays whole.

For UK-outbound assignees to France, Belgium, or Italy, the gross-up uplift on the host tax payment runs 30 to 60 per cent. See the tax equalisation entry for the full policy mechanic and the hypothetical tax entry for the deduction that sits on the home payroll side.

How much does gross-up actually cost the employer?

The headline net figure is always the smallest line on the calculation. The country sets the multiplier between net and total employer cost.

Figures are indicative. Exact gross-up depends on the assignee's full year-to-date position and any country reliefs. The pattern holds: a £10,000 net promise in France costs roughly 2.75 times more than the net delivered, against 1.85 times in the UK.

For accurate scenario modelling, the employer cost burden calculator covers the per-country loading on grossed-up payments and ties into the employer contributions picture.

What should payroll buyers check before approving a gross-up?

One internal checklist, one provider checklist. Both fit on a single page.

Payroll buyer checklist

• Is the payment quoted as net to the employee or gross to payroll?
• What marginal income-tax rate applies once year-to-date earnings are included?
• Do employee social-security contributions still bite at this band?
• Are local surcharges (solidarity, high-income, regional) in scope?
• Is the payment routed through standard payroll or a PSA-style return?
• What employer-side contribution loading applies on the grossed-up figure?
• Has total cost been signed off before the offer letter goes out?
• Is the year-end reconciliation owned by payroll, mobility, or finance?

Questions to ask your EOR or payroll provider

• Does the standard payroll engine iterate gross-up automatically?
• Will you flag when a benefit pushes the employee into a new band?
• How do you handle gross-up on assignments under tax equalisation?
• Are PSA-route benefits supported, or is that an in-house responsibility?
• How is the year-end true-up handled, and what does it cost?

Gross-up FAQs

Is gross-up the same as tax equalisation?

No. Gross-up is a payroll calculation that inflates a gross figure so the net hits a target. Tax equalisation is a mobility policy that uses gross-up as one of its tools, alongside hypothetical tax and shadow payroll. Every equalised assignment includes gross-up; not every gross-up implies an equalisation policy.

Do bonuses always need to be grossed up?

Only if the offer or policy quotes the bonus as a net figure. Most bonuses are paid as a gross amount and run through normal gross-to-net payroll, with tax and contributions reducing the net the employee receives. Net-quoted sign-on or retention bonuses force the gross-up calculation; gross-quoted bonuses do not.

How does gross-up work on benefits-in-kind?

In the UK, employers can settle tax on minor or irregular benefits through a PAYE Settlement Agreement. HMRC PAYE76000 sets out the rules. The employer pays the employee's tax at the marginal rate, grossed up so the tax itself is covered, then adds Class 1B NI at 15 per cent on the grossed-up figure. The benefit lands as fully tax-cleared, with all cost on the employer side.

Does an EOR handle gross-up?

Yes for standard payroll gross-up: bonuses, benefits, and one-off lump sums run through the local payroll engine. Tax-equalisation gross-up on global mobility assignments usually sits with a separate Big Four or boutique provider, billed per assignee. Check the EOR scope before assuming the full mobility workflow is covered.

What is the simplest gross-up formula?

Gross equals net divided by one minus the marginal effective rate. For a £10,000 net to a UK higher-rate taxpayer at 42 per cent combined income tax and employee NI, gross is 10,000 / 0.58, or roughly £17,241. Employer NI then lands on top of the gross. If the payment crosses a tax band, payroll iterates the calculation until the net hits target.