These voluntary contributions are known as 'buy-backs' and represent the pension contributions that you 'missed', prior to your current Swiss employment start date, as far back as age 25 and, importantly, using your current salary. This applies to both those who have lived in Switzerland their entire lives, and those who are expats.
The key advantage of voluntary ('extra-mandatory') Pillar 2 contributions is the immediate income tax-relief.
As the calculation on your maximum buy-back limit is based on your current salary, and your salary would be expected to be higher as you gain more years of experience, the tax saving effect is often optimal when your income is at its highest point. Usually, this is a few years before retirement.
Keep in mind that the same tax advantages apply to your Pillar 3a contributions and so, as that allowance is a 'use it or lose it' allowance each year, ensuring you have paid into your Pillar 3a before making buy-back payments is worth considering.
Should you decide to make any buy-backs, your entire fund will be tied up for 3-years under Swiss pension rules, from the date of your last buy-back payment. This is especially important if you are nearing retirement and looking to withdraw the funds within that time, as you may not wish to be restricted in accessing the funds.
You should receive a Pillar 2 statement from your Provider each year (usually in January). On this statement, you can find your maximum buy-back allowance. You are able to pay any amount you like, up-to that maximum.
The answer as to whether you should make voluntary contributions, or not, is down to many factors, including:
Please note that all content within this response has been prepared for information purposes only. This response does not constitute financial, legal or tax advice. Always ensure you speak to a regulated Financial Adviser before making any financial decisions.