Shadow payroll for cross-border assignees

Moving an employee abroad creates tax duties in the host country, often from the first day of work. A shadow payroll meets those duties without changing how the employee gets paid. This guide explains when you need one, how tax equalisation works and what the UK modified payroll scheme involves.

What is a shadow payroll?

A shadow payroll is a host-country payroll that reports an assignee’s income and withholds local tax. Meanwhile, the employee keeps receiving salary from the home payroll. In other words, the shadow payroll mirrors the home payroll without paying the employee directly.

For example, a Dutch engineer seconded to London stays on the Dutch payroll. A UK shadow payroll then calculates PAYE and pays it to HMRC. In turn, the Netherlands gives relief against double taxation. For this reason, shadow payroll sits at the heart of expatriate payroll.

When does a cross-border assignment need a shadow payroll?

You usually need a shadow payroll when the host country taxes the assignee’s pay and requires local withholding. That depends on the length of stay, who bears the salary cost and the tax treaty. Therefore, assess every assignment before travel.

The 183-day rule and the economic employer

Most tax treaties follow Article 15 of the OECD Model Tax Convention. Under it, pay stays taxable only at home when three conditions apply. First, the employee spends no more than 183 days in the host country in any 12-month period. Second, the employer is not resident there. Finally, no local permanent establishment bears the salary cost.

However, the exemption often fails in practice. For instance, many groups recharge assignee costs to the host entity. Authorities may then treat it as the economic employer, so local tax can apply from day one.

Social security follows separate rules

Under the EU posting rules, posted workers can keep home social security for up to 24 months. A Portable Document A1 proves it. However, an A1 covers social security only, not income tax. Octagon’s guide to A1 certificates for cross-border employees explains how to apply.

How does tax equalisation work with shadow payroll?

Tax equalisation keeps the assignee’s tax cost roughly equal to what they would pay at home. The employer deducts a hypothetical home-country tax from salary. In turn, it pays the actual host-country tax through the shadow payroll. As a result, the move stays tax-neutral for the employee.

However, tax the employer pays counts as extra taxable income, so the shadow payroll must gross it up. Local incentives matter too. For example, assignees moving to the Netherlands may qualify for the 30% ruling. From 1 January 2027, the rate drops to 27%, except where transitional rules apply. Octagon’s 30% ruling savings calculator estimates the effect.

What is a modified payroll scheme?

A modified payroll scheme is an HMRC arrangement for tax-equalised employees assigned to the UK. HMRC calls it modified PAYE under EP Appendix 6. The employer runs PAYE on a best estimate of annual earnings and benefits, grossed up for tax. Consequently, the employee does not need to make payments on account.

Under HMRC’s guidance on tax equalisation arrangements, the employee reports actual figures by 31 January after the tax year. Any balance then becomes due. Moreover, the employer must make good underpayments caused by its own errors. Employers can also apply for modified National Insurance under EP Appendix 7A.

Shadow payroll compared with other expatriate payroll models

Shadow payroll is one of three common expatriate payroll models. The others are split payroll and localisation, including employment through an employer of record. The right choice depends on assignment length and whether you have a local entity.

Model	Who pays the employee	Tax withholding	Typical fit
Shadow payroll	Home payroll	Host payroll; home country gives relief	Temporary assignments
Split payroll	Both payrolls, each paying part	Usually both, each reflecting the other’s payments	Costs in two countries
Localisation or employer of record	Host employer or employer of record	Host payroll	Long-term moves or no local entity

How do you set up a shadow payroll?

Set up the shadow payroll before the assignee starts work abroad. First, confirm the tax and social security position. Then register locally and agree a monthly data flow. Finally, plan the year-end reconciliation from day one.

1. Track workdays and review the relevant tax treaty.
2. Secure an A1 certificate or register for local social security.
3. Register as an employer or withholding agent locally.
4. Share pay, benefit and exchange-rate data monthly.
5. Apply your tax equalisation policy and gross-up rules.
6. Reconcile both payrolls and issue local year-end statements.

Moving talent across borders with confidence

Handled well, shadow payroll protects employers from back taxes, penalties and double taxation. Just as importantly, assignees can focus on their work rather than their tax position. Octagon Professionals International has helped organisations move people across borders since 1987.

Its HR experts handle expatriate payroll administration and A1 certificates across Europe and the UK. They also manage 30% ruling applications in the Netherlands. Where a secondment is not the best route, Octagon can act as employer of record. Throughout, you keep full control over salary, benefits and working arrangements. In short, Octagon enables talent to move across borders with clarity, compliance and trust.

Planning an international assignment? Contact Octagon to review your assignees before they travel.

Frequently asked questions about shadow payroll

What is the difference between shadow payroll and split payroll?

With shadow payroll, the employee receives their full salary from the home country. The host payroll only reports income and pays local tax. With split payroll, each country pays part of the salary. Companies often choose split payroll when assignees have living costs in both locations.

Do I need a shadow payroll if my employee has an A1 certificate?

Possibly. An A1 certificate only confirms which country collects social security contributions. It says nothing about income tax. So if the host country taxes the salary locally, the employer may still need a payroll there. The A1 reduces the work but rarely removes it.

Is shadow payroll required for short business trips?

Not always. Most tax treaties keep pay for stays of up to 183 days taxable only at home. However, this requires a foreign employer to pay the salary, with no local entity bearing the cost. Some countries also apply stricter local rules, so track travel days carefully.

Who pays the tax under a tax equalisation policy?

The employer pays the actual host-country tax. Meanwhile, the employee contributes a hypothetical tax, roughly equal to their home-country liability. After the tax year, a settlement calculation corrects any difference. As a result, the assignee’s net pay stays broadly the same as at home.