As stated Maternity Benefit is Liable to Tax since 2013.What needs to be ascertained is how your employer will determine what happens to your maternity benefit whilst on maternity leave, in other words what terms and conditions do they set out in your contract of employment. There are two ways employers may treat maternity benefit.
1) You may receive your full Salary/Pay/Wages as normal, but they will request you to sign the maternity benefit over to them.In this case your Payroll Department will adjust your salary to reflect this. The equivalent result of this is your Salary LESS MATERNITY BENEFIT will determine the correct amount of Tax to be deducted e.g. Normal salary say €2,500.00c Benefit €900.00c (Monthly Figures Used Here) so the balance is €1,600.00c Add back the the Benefit €900.00c and then you are liable to be taxed on only €2,500.00c (The Adjusted Salary plus Benefit) Payroll then can run it properly on a cumulative basis. It should be noted that The USC Charge and the PRSI Deductions only APPLY to the €1,600.00c adjusted salary.
2) If your employer does not pay Salary during Maternity Leave,then you receive the Benefit in full (Still Liable to Tax). Of course your SRCOP and Tax credits will need to be adjusted to properly deduct tax for the receipt of benefit, however you will need to do this yourself by contacting the Revenue office of where you live.The year end Income from all sources is totaled and reflected on your P60. With this you can request a P21 Balancing statement, which gives the result of Taxes USC, PRSI deducted.Please note the adjusted SRCOP Tax Credit Cert will ensure the correct taxes are deducted in relation to the Benefit, if your employer does not pay you your normal salary.
Do ascertain the Terms and conditions of your employment in relation to Maternity Benefit, from your H.R.Department.