The 183 days rule may not always be correct, it is just like relying on half knowledge which could be more dangerous. As a standard rule, host (or source) country where the assignment is exercised has the first right to tax the assignment income. Due to assignee’s nationality and residency, there may be a situation that he is taxable in the host as well as the home country. In such situation, relief under the bilateral tax treaties may be sought which provides for short stay exemption from taxing the assignment income in the host country, if following conditions are met:
The assignee stays in the host country for 183 days or less during the year
The assignee is remunerated by an employer who is not a resident of the host country (e.g home entity)
Such remuneration is not ultimately borne by employer’s permanent establishment (PE) in the host country (home entity’s PE in the host country)
It may be noted that the aforesaid exemption has limited applicability. If the expats are remunerated in the host country or if the cost is ultimately borne by the host entity, then applying the 183 day rule would go otiose