In Ireland, when you contribute to your pension, the amount is deducted from your gross pay, not your net pay. This means you're benefitting from tax relief: you're not getting taxed on what goes into your pension pot when you're contributing.

The decision on how much you contribute per month to your pension should take into consideration lots of things like your age, your income, your retirement plan, etc. This is independent of how much your employer will be contributing - see here how to contribute with a different percentage than your employer's. Ultimately, the judgment lies with you. 

You can use this Pension calculator provided by Irish Life - our pension provider in Ireland - to help you decide what percentage you would like to contribute to your retirement fund each month.