Last reviewed July 2026. General guidance, not personalised advice. For your situation, book a free consultation.

Preliminary tax catches a lot of first-time self-assessed people by surprise. Here's what it is and how to avoid paying interest.

What is preliminary tax?

It's an advance payment towards your current year's income tax, USC and PRSI. Rather than waiting until after the year ends, Revenue asks self-assessed taxpayers to pay an estimate up front.

Who pays it?

Anyone in the self-assessment system — sole traders and others who file a Form 11.

When is it due?

On the same pay & file date as your return — 31 October, or the extended ROS deadline (18 November 2026 for the 2025/2026 cycle). You pay it alongside any balance owed for the previous year.

How much to pay to avoid interest

To stay in the clear, pay at least the lowest of:

  • 90% of your final liability for the current year, or
  • 100% of your liability for the previous year, or
  • 105% of the liability for the year before that (this option is only for those paying by direct debit).

Most people use the 100%-of-last-year option because it's the easiest to calculate with certainty. Underpay and Revenue can charge daily interest on the shortfall.

In your first year of self-assessment you can end up paying two amounts at once — plan for it early.

The first-year squeeze

Here's the catch that surprises people. In your first pay & file, you settle the balance for last year and pay preliminary tax for this year at the same time — potentially close to two years' tax in one go. It's not extra tax, just timing, but it's worth setting money aside early so the bill isn't a shock.

We help clients estimate preliminary tax and set aside the right amount through the year, so there are no surprises in October. Talk to us and we'll take the guesswork out of it.

Sources: Revenue.ie and Citizens Information (self-assessment and preliminary tax).