The paper filing deadline has been pushed back by a week to Thursday, 14 November.
Almost one million homeowners liable for property tax received letters from Revenue in recent weeks asking them to choose a method of payment for 2014.
Those choosing to file their returns by post had until tomorrow to do so. However, Revenue has now extended that deadline.
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The online deadline remains 27 November.
The opening hours of the tax helpline – 1890 200 255 – have also been extended to deal with queries from the public.
The helpline will be open from 8am to 8pm from today onwards.