Start with social security affiliation
A contract signed in Geneva, days working remotely in France and tax withheld from Swiss pay answer different questions. The Federal Social Insurance Office says pillar 3a generally requires employment or self-employment income subject to Swiss OASI. An A1 certificate identifies the social security legislation applicable to the situation and period it covers. It is neither proof of a payment into pillar 3a nor a decision accepting that payment as a tax deduction.
Why the same weekly timetable can produce different results
Suppose someone lives in France, works from home two days in five and spends the rest of the week in Geneva with one Swiss employer. Forty per cent is within the range covered by the framework agreement for habitual telework between signatory countries, provided all conditions are met. The employer must apply for the relevant certificate. If the worker also regularly carries on self-employment in France or makes regular business visits there, the federal guidance identifies exclusions from the agreement. The whole pattern of work needs to be assessed.
Read the dates and assumptions on the paperwork
Ask your employer for the A1, its validity dates and the work split declared on the application. Compare that with where you actually work, whether you have another employer and when any side business started. If your schedule changes during the year, record the dates and ask whether you need a fresh determination. Contributions still appearing on a payslip do not, by themselves, settle a change of affiliation.
Treat tax relief as a separate question
If the compensation office confirms that you remain under Swiss social security and the earnings qualify, check the permitted contribution with your 3a provider. Whether it is deductible in your particular cross-border tax situation then needs its own review. For example, someone considering CHF 300 a month should budget CHF 3,600 a year without assuming tax relief that has not been confirmed. An A1 alone does not establish whether subsequent ordinary assessment in Geneva is available or worthwhile.
Prepare one file before making a commitment
Gather your work calendar, employment contract, affiliation decision, salary certificates and the period in question. Ask the employer or compensation office which social security system applies, the foundation whether it accepts the contribution, and a tax adviser where and on what terms the amount might be deductible. Keeping those answers separate tells you who to ask again if you increase your remote hours.