Take-home working abroad depends on where you are tax resident, which is decided by rules rather than by preference and usually turns on days present and where your permanent home is. Most countries tax residents on worldwide income and non-residents on local income only, with treaties preventing the same income being fully taxed twice. Social security is governed separately, by its own agreements.
Residency is the first question, not the second
Almost everything else follows from it. Residency is determined by tests — days present, where your permanent home is, where your center of vital interests sits — and it is possible to satisfy the tests in two countries at once, which is what treaty tie-breaker rules exist to resolve.
It is not a matter of what you tell anyone. It is a factual determination and it can be established in advance.
The general shape
Residents are generally taxed on worldwide income. Non-residents are generally taxed only on income sourced in that country. Where both countries have a claim, a double taxation treaty allocates it, usually through a credit or an exemption, so the same income is rarely fully taxed twice — but “rarely fully” is not “never at all”, and the residual can be material.
Social security is a separate system
It has its own agreements, often called totalisation agreements, and they do not necessarily follow the tax treaty. It is entirely possible to be tax resident in one country and contributing to another’s social security. Getting this wrong can mean paying twice, or worse, contributing to a system you will never draw from.
Whether contributions count toward a pension you can actually receive is the question worth asking, and it has a documented answer per country pair.
What employers frequently get wrong
Assuming a domestic payroll can simply pay someone abroad. In most cases it cannot, which is why employers use local entities or employer-of-record arrangements. Where a role is offered without either being in place, the tax exposure usually lands on the employee.
Before accepting
Establish which country you will be tax resident in and from when. Establish which social security system you will contribute to and whether it counts toward a pension you can claim. Establish who is responsible if the arrangement is wrong. And get the net figure at your actual position rather than the gross, because gross across two tax systems compares nothing.
All four are answerable in advance and expensive to discover afterwards.
Common questions
What decides which country taxes me?
Tax residency, determined by tests u2014 days present, where your permanent home is, where your center of vital interests sits. It is a factual determination, not a choice.
Will I be taxed twice?
Rarely in full. Double taxation treaties allocate the claim between countries, usually via a credit or exemption, but a residual can remain and it can be material.
Is social security covered by the tax treaty?
No. It is governed by separate agreements, and it is entirely possible to be tax resident in one country while contributing to another's system.
Will contributions abroad count toward my pension?
Sometimes, under a totalisation agreement, and sometimes not at all. It has a documented answer per country pair and is worth establishing before you accept.
Can my current employer just pay me abroad?
Usually not without a local entity or an employer-of-record arrangement. Where neither is in place, the tax exposure typically lands on the employee.