Social Security When You Work Across Borders (2026)

If you have read the double taxation treaties guide, you know how two countries divide the right to tax the same income. None of that applies here. Social security sits outside tax treaties, runs on its own instruments, and answers a different question: not who taxes you, but whose system you belong to.

It is also, in several of the countries this site covers, the larger bill.

The bills are not small

Country	What a self-employed person contributes
Portugal	21.4% of relevant income — about 15% of gross for a services freelancer
Spain	A monthly cuota from €205.88 to €607.35 by income tramo, including MEI
Estonia	Nothing on retained profit; board-member fees carry 22% withholding
Georgia	Voluntary pension opt-in only
UAE	Nothing for expatriate residents
Singapore	No CPF for foreign work-pass holders

Portugal’s social security costs a freelancer more than their income tax does at ordinary earnings. Spain’s cuota is payable whether or not you invoiced anything that month. Meanwhile three of the six charge nothing at all. The spread between the top and bottom of that table is wider than the spread in income tax rates — which is why the question of which system you fall into is worth answering deliberately rather than by default.

One country at a time

Within the EU, plus Iceland, Liechtenstein, Norway and Switzerland, coordination runs on Regulation 883/2004. Its governing principle is that you are subject to the social security legislation of one country at a time, never two and never none.

That sounds obvious and is the opposite of how tax works. You can be tax resident in two countries simultaneously and rely on a treaty tie-breaker to sort it out. You cannot be socially insured in two member states at once. The regulation picks one.

The general rule is that you are covered where you actually work, not where you live and not where your client is. Three situations modify it.

You work in one country for an employer in another. You are covered where the work is performed.

You are posted temporarily. If your employer sends you to another member state, or you are self-employed and go to work temporarily in another member state, you can stay in your home system. The A1 certificate for this is issued for a maximum of 24 months. After that you either move into the host country’s system or the two authorities have to agree an extension between them.

You work in two or more countries. This is the case most remote workers are actually in, and it has a threshold. You remain covered by your country of residence if you carry out a substantial part of your activity there — defined as at least 25% of working time and/or income. For a self-employed person, turnover and the services provided are also weighed. Fall below 25% in your country of residence and the answer changes, typically to where your employer or business is based.

That 25% figure is the single most useful number in this guide. It is the line between “I live here, so I am insured here” being true and being an assumption.

Your situation	Whose system covers you	Document
Working in one country, employer in another	Where the work is performed	—
Posted abroad temporarily by your employer	Your home country	A1, max 24 months
Self-employed, working temporarily in another member state	Your home country	A1, max 24 months
Working in two or more countries, at least 25% of activity where you live	Your country of residence	A1
Working in two or more countries, less than 25% where you live	Generally where the employer or business is based	A1

The bottom two rows are where remote workers actually live, and the difference between them is not a matter of degree. Crossing the 25% line moves you between two entire systems — different contribution rates, different registration, different pension entitlements — on the basis of how your working time happened to distribute across a year.

The A1 certificate is the proof

A PD A1 is a statement of applicable legislation. It is issued by the institution in the country whose system covers you, and it exists so that another country’s authorities can see you are already contributing somewhere and should not be charged again.

It is issued by your home institution if you are posted, and by your country of residence if you work in several states at once. It is not a formality in practice: inspections in some member states ask for it directly, and an absent A1 is treated as evidence that contributions are owed locally, with the burden falling on you to prove otherwise after the fact.

Apply before you go, not after you are asked.

Outside the EU it is bilateral or nothing

The coordination regulation covers the EU/EEA and Switzerland. Beyond that there is no general system. Countries sign bilateral social security agreements — often called totalisation agreements — one pair at a time, and their coverage is uneven.

Where such an agreement exists between your country and the one you are working in, it usually does two things: prevents double contributions, and lets periods insured in one country count toward qualifying for a pension in the other. Where none exists, both outcomes are lost. You may be liable in both places at once with no mechanism to prevent it, and years of contributions in one country may simply not count toward anything in the other.

This is a genuine asymmetry with tax. A tax treaty missing between two countries is inconvenient, and unilateral foreign tax credits usually soften it. A social security agreement missing between two countries has no equivalent fallback.

What this means in practice

Three habits prevent most of the trouble.

Work out which system covers you before you move, not after, because the answer determines where you register and registration is much harder to backdate than to arrange.

Hold the A1 if you are inside the EU and working across borders, including if you are self-employed and simply spending months in another member state.

Check whether an agreement exists at all if either country is outside the EU/EEA, and treat its absence as a real cost rather than a technicality — both the double contributions and the lost pension years are money.

And when comparing countries by what they leave you, count contributions rather than only tax. Our five-country net income comparison includes them, which is why its ranking differs from what income tax rates alone would suggest.

What this guide does not cover

Contribution rates change annually and the figures above are verified for 2026 for the countries this site models. They describe the self-employed position; employed people have employer contributions on top, which are frequently larger than the employee share and invisible on a payslip.

The regulation’s detailed rules on multi-state activity are more intricate than a 25% threshold implies — mixed employed and self-employed activity in different states, or activity in three or more states, follow specific provisions in Regulation 883/2004 that this summary does not attempt to reproduce. Where the answer matters financially, it is decided by the institution in your country of residence, and asking them is the reliable route.