What is preliminary tax?

Revenue's Pay and File system means that, by the October deadline, a self-assessed person generally files the return for the previous tax year, pays any balance for that previous year and pays preliminary tax for the current year.

This advance payment is called preliminary tax. It is not a penalty or an extra charge — it is simply a deposit against a tax bill that has not been finalised yet. When you file next October, you pay the balance of what you actually owe after crediting the preliminary tax you already paid.

How to calculate preliminary tax

Revenue allows three methods. The required amount must be at least the lowest of the following Revenue tests:

MethodHow it worksWhen it is commonly used
Method 1Pay 100% of the tax due for the immediately previous tax yearUses the previous year's final liability rather than estimating the current year
Method 2Pay 90% of the tax due for the current tax yearUses an estimate of the current year
Method 3Pay 105% of the tax due for the pre-preceding yearOnly applies where payment is made by direct debit and the pre-preceding year liability was not nil

Source: Revenue.ie — Preliminary tax ↗

If a preliminary tax payment is below the required Revenue amount, Revenue can charge interest on the shortfall. The method used affects how that required amount is tested.

First-year and Pay and File timing

Revenue says a payment of preliminary tax may not be required for the first year a person is self-assessed. If the 100% previous-year method is used, the previous year's liability would normally be nil in that first year.

The cash-flow issue often appears at the first Pay and File deadline after a trading year, because the same deadline can include both:

What may be due at the first Pay and File deadlineAmount (example)
Balance of the previous tax year's liability€4,000
Preliminary tax for the current tax year€4,000
Total due in one payment€8,000

This is not a mistake or a penalty. It is a timing feature of the Pay and File system. Actual figures can differ because profit, credits, PRSI, USC, previous payments and the preliminary tax method all affect the calculation.

Some sole traders keep a percentage of each payment in a separate account during the year. The amount needed depends on income, expenses, credits, USC, PRSI and the final tax calculation.

What this means in real life

For a sole trader, preliminary tax means that an October payment can cover two different periods at once: the balance for the previous tax year and an advance amount for the current year. This is why the second year of self-assessment can involve a larger cash requirement even when the business has not suddenly become more profitable. The preliminary amount is credited against the final liability for that year when the return is later filed; it is not an extra lifetime tax. Revenue allows different calculation methods, but underpaying against the required test can lead to interest. The practical figures depend on actual profit, credits, earlier payments and the method used. The sole trader tax guide explains the wider income tax, USC and PRSI position.

Common confusion

No. It is a deposit toward the current year's bill, not an additional charge. When you file next year's return, your preliminary tax is credited against your final liability. If you overpaid, you get a refund or credit. The total tax you pay over your lifetime as a sole trader is the same — preliminary tax just changes the timing.
Revenue says a preliminary tax payment may not be required for the first year a person is self-assessed, because the previous year's liability would normally be nil under the 100% previous-year method. A later Pay and File deadline can still include the previous year's balance and preliminary tax for the current year.
This depends on the estimate used. If Method 2 (90% of current year estimate) is used and the estimate is too low, Revenue can charge interest. Revenue also lists a 100% of previous year liability method, which avoids estimating the current year.