Preliminary tax: the lowest safe amount

Pay the lowest of 90% of this year's tax, 100% of last year's, or 105% of the year before (direct debit only) to avoid interest.

Preliminary tax is your payment on account of the income tax, USC and PRSI you expect to owe for the year. It is due by 31 October of that year, with the ROS extension when you pay and file online.

How much is enough

To avoid interest, pay at least the lowest of:

• 90% of the tax due for this year
• 100% of the tax due for last year
• 105% of the tax due for the year before last, only if you pay by direct debit, and not if that year's tax was nil

100% of last year is the safe choice when this year is going better: it avoids interest however high this year's bill turns out. If this year is worse, 90% of this year's estimate costs less now, but an estimate that proves too low means interest.

Your first year

In your first year of self-assessment, last year's self-assessed tax is usually nil, so you often don't need to pay preliminary tax. The full bill then arrives the following October, together with the next year's preliminary tax. Paying something voluntarily spreads that out.

Work it out

• Preliminary tax →
• Sole trader tax return →

Sources

• Revenue: What is preliminary tax? (checked 25/10/2026)
• Revenue: Pay and file system: how does it work? (checked 25/10/2026)

General information, not tax advice. HeyPenny is not a tax agent.