Why Has My Tax Code Changed? Ireland 2026 Tax Guide

You open your payslip and the number looks wrong. More tax, fewer credits — but nothing in your life has changed. That sudden shift usually traces back to one of a handful of known triggers, and in Ireland the most common culprit right now is a move onto what Revenue calls the “Week 1 basis.” The good news: it’s usually fixable in days once you know where to look.

Standard Irish tax bands: 20% up to €42,000, 40% above · Week 1 basis trigger: New job or mid-year change · Budget 2026 changes: Announced by Tánaiste, effective 1 Jan · Tax credit certificate: Issued on Week 1 basis · Revenue.ie login for check: Manage My Tax Credits

Why has my tax code changed?

When your tax code on your Tax Credit Certificate (TCC) shifts, Revenue has acted on new information about your income or personal circumstances. The most common reason for an apparent change is a switch to the Week 1 basis of taxation.

Common reasons from Revenue.ie

Revenue assigns Week 1 basis when your records are incomplete or when your employment circumstances change mid-year. According to Revenue’s employer guidance, employers must use Week 1 basis if instructed via an RPN (Revenue Payroll Notification). This means your Tax Credit Certificate now specifies Week 1, and your employer deducts tax week-to-week without accumulating your yearly credits from January.

Impact of new job or income change

Starting a new job is the most common trigger. Your new employer has no prior earnings data, so Revenue issues a Week 1 basis TCC. Your tax credits do not accumulate week-to-week — each pay run is taxed as if it were week one of the year. FinanceTool.ie notes that this often results in higher initial PAYE deductions compared to the cumulative method. A rise in income, additional employment, or a change in tax credits can also prompt Revenue to update your TCC mid-year.

Why am I on week 1 basis?

Week 1 basis — also called Month 1 for monthly-paid employees — means your employer calculates tax on each pay period independently, without applying year-to-date earnings or credits. Revenue.ie defines it as a non-cumulative approach where tax and USC are deducted week-to-week, ignoring what you may have already earned or what tax credits you are entitled to for the full year.

When Week 1 basis applies

Revenue issues Week 1 basis on your TCC when your employer receives an RPN directing it, typically after a job start, a mid-year change, or when your previous tax records are unavailable. It is not emergency tax — it is a standard tax basis that applies until a cumulative TCC is issued. Revenue’s employer instructions make clear that on Week 1 basis, employers cannot refund overdeducted Income Tax or USC until a cumulative TCC arrives.

Difference from cumulative tax

The alternative is cumulative basis, which accumulates your earnings and tax credits from 1 January to ensure correct tax and full benefit of your credits throughout the year. Revenue.ie explains that cumulative basis gives you the most accurate tax position if you have been with the same employer since the tax year began. Week 1 basis is the default when Revenue lacks full-year data; it is not a penalty, but it does front-load deductions.

What are the tax changes in Ireland in 2026?

Budget 2026 introduces several PAYE changes that took effect from 1 January 2026. The most direct impact on most workers is the adjustment to Universal Social Charge (USC) bands, which the Tánaiste announced as part of the government’s policy to keep full-time minimum-wage earners outside higher USC bands.

Budget 2026 announcements

The USC 2% rate band ceiling increases from €27,382 to €28,700 from 1 January 2026. Sage KB confirms the full 2026 USC structure: 0.5% up to €12,012, 2% from €12,012.01 to €28,700, and 3% from €28,700.01 to €70,044. From 1 October 2026, the PRSI threshold rises from €527 to €552 per week, with employer and employee rates increasing by 0.15%.

To continue the government’s policy of ensuring that full-time workers on the minimum wage will remain outside the charge to the top rates of USC, the ceiling of the 2 per cent USC rate band has increased to €28,700. — Simon Harris, Tánaiste and Minister for Finance (Gov.ie Budget announcement)

On Week 1 basis, employers cannot refund overdeducted Income Tax or USC until a cumulative Tax Credit Certificate is issued by Revenue. — Revenue Commissioners (Revenue.ie employer guidance)

Effects on tax codes and bands

These band changes do not automatically alter your tax code, but they can trigger a Revenue review of your tax position — particularly if your income crosses a threshold or if software updates recalculate your deductions. Sage’s legislation analysis notes that payroll software updates for 2026 USC and PRSI changes may affect tax code calculations for employees whose positions are close to a band boundary.

How do I change my tax code online?

Ireland’s Revenue Online Service (ROS) gives you direct access to your tax records. The Manage My Tax Credits section within myAccount lets you view your current TCC and see whether it is set to Week 1 or cumulative basis.

Steps via Revenue.ie

1. Log into myAccount on Revenue.ie
2. Navigate to Manage My Tax Credits
3. Check your Tax Credit Certificate details — look for the basis stated
4. Use the MyEnquiries facility to contact Revenue if your TCC shows Week 1 incorrectly
5. Provide any missing documentation (P45, previous payslips) via the secure messaging system

Contacting employer or Revenue

If your TCC is correct but your employer is not applying it properly, contact your payroll department with your Tax Credit Certificate number. If Revenue has issued Week 1 basis in error, Revenue’s employer guidance notes that your employer cannot refund overdeducted tax until a cumulative TCC is issued — so the fix must come from Revenue first.

How do I change from week 1 basis to cumulative?

Switching from Week 1 to cumulative basis requires Revenue to issue an updated Tax Credit Certificate showing cumulative. Your employer then applies it from the next payroll run.

Request cumulative basis

Contact Revenue via MyEnquiries in myAccount, explaining that you are on Week 1 basis and requesting a cumulative TCC. Include your employment details and, if available, your P45 from your previous employer or evidence of year-to-date earnings. Revenue.ie advises that if you are still on Week 1 basis at year-end, you should submit an Income Tax Return via PAYE Services in myAccount for review.

What to tell your employer

Once Revenue issues the cumulative TCC, your employer receives an updated RPN automatically. You do not need to give your employer a physical certificate — the RPN carries the correct basis. If weeks have already passed under Week 1 basis, any overpayment will be reconciled when the cumulative basis kicks in, and any refund will come through your payroll once a cumulative TCC is active.

Related reading: How Much Can You Put in an ISA · Universal Credit 325 Payment

Tax code alterations in Ireland often follow Budget 2026 measures that kept personal tax allowance rates and bands steady at 2025 levels for most workers.

Frequently asked questions

For PAYE workers caught in a Week 1 basis situation, the path forward is straightforward: get your records to Revenue, wait for the cumulative TCC, and let reconciliation sort itself through payroll. The implication of Budget 2026 is broader — the USC band shift protects lower earners, but anyone earning near the €28,700 ceiling should monitor their payslip once the new bands apply from January.