The first thing to establish is not the rate. It is which country has the right to tax the pension at all, and that depends on the applicable double tax treaty and on the kind of pension.
- Private and occupational pensions are, under most treaties, taxable only in the country of residence. Move to Italy, and Italy taxes them.
- Government service pensions usually behave the opposite way: they typically remain taxable only in the paying state, whatever your residence. This catches a great many former civil servants, teachers and military personnel by surprise.
- State social security pensions vary by treaty and have to be checked individually rather than assumed.
The practical consequence is that two neighbours in the same Italian town, both retired, both drawing the same amount from the same country, can face completely different Italian tax positions.