Annual road tax in Ireland uses different regimes, depending on the date of registration. It uses the old regime, which uses the vehicle engine capacity for tax computation and which applies to vehicles registered in Europe prior to July 2008. It also uses a system whereby the engine size rule was ditched in favour of calculating the tax based on how much carbon dioxide the vehicle releases. This would be a way to encourage people to buy cars with lower CO2 emissions. This system applies for cars registered after 2008.

The tax using the cylinder capacity amounts to 199 euros to 1,810 euros for cars with a engine capacity from 1,000 cc to 3,001. Electric vehicles must pay 120 euros flat. As an example, a driver of a vehicle with a small 1,100 cc engine must pay 299  euros, while someone driving a car with a large 3,001 cc engine pays 1,809euros a year.

Under the new regime, the tax is determined on the basis of CO2 released emissions. The bands are categories which classify cars depending on their CO2 released emissions. These bands range from A to G. Cars releasing emissions from 1 to 80 g/km must pay 170 euros tax. The maximum tax rate is for cars releasing from and above 226 g/km CO2 and amounts to 2,350 euros. Though electric vehicles do not release tailpipe emissions, they are also subject to a 120 euros tax. There are some exempted vehicles among which vehicles falling under the scope of the Disabled Drivers and Disabled Passengers Regulation.

From January 1st, 2021, following the Minister for Finance new Budget 2021, a new CO2 tax rate has been introduced following the EU emissions test for passenger cars for newly registered cars. The tax rate is based on the Worldwide Harmonised Light Vehicle Test Procedure (WLTP) CO2 emissions and only impacts vehicles that fall into bands C to G (from 10 euros for bands C to 50 euros for Band G). The rise in tax rates means that those who buy new cars with above average emissions will be forced to pay more. As a result, the government has hopes that this change will encourage people to buy more eco-friendly cars.