Seen "Week 1" or "Month 1" on your payslip? This tax code means you're on what's called a non-cumulative or Week 1 basis—and it's often a sign you've been overpaying tax. While it's sometimes applied temporarily, many workers stay on Week 1 basis for months without realising they're losing money.
Our specialists regularly help clients who've been stuck on Week 1 basis recover significant overpayments. Here's what you need to know.
📊 Week 1 Basis Key Facts
- What it means: Tax calculated on each pay period independently
- Common cause: Job change or incomplete tax details
- Problem: You don't benefit from cumulative credits
- Solution: Claim back overpaid tax
What Is Week 1 Basis?
Normally, your tax is calculated on a cumulative basis—meaning your tax credits and rate band build up throughout the year. If you've paid too much tax in earlier months, later payslips adjust to give you a refund.
On Week 1 basis, each pay period is treated independently. Your weekly or monthly tax credits are applied, but there's no cumulative calculation. This means:
- Overpayments from earlier in the year aren't automatically refunded
- You can't benefit from unused credits from previous weeks/months
- You often pay more tax than you should over the year
Why Are You on Week 1 Basis?
There are several common reasons:
Job Change
When you change jobs, Revenue sometimes issues Week 1 instructions to your new employer while they sort out your tax details. This is meant to be temporary but can persist.
First Job
Starting your first job without proper tax registration often results in Week 1 or emergency tax.
Revenue Uncertainty
Sometimes Revenue puts you on Week 1 basis if there's uncertainty about your tax situation—for example, if you have multiple employments or they need to verify information.
💡 Real Example
Cathy changed jobs in March and was placed on Week 1 basis. She didn't notice until October. By then, she'd overpaid €780 in tax—money she would have received back automatically on cumulative basis. Our review claimed it all back for her.
How to Know If You're on Week 1 Basis
Check your payslip. If you see:
- "Week 1" or "W1" for weekly pay
- "Month 1" or "M1" for monthly pay
You're on non-cumulative basis. Also check your Tax Credit Certificate—it will indicate if Week 1 basis applies.
Getting Your Money Back
If you've been on Week 1 basis, you're likely owed a refund. Our specialists will:
- Review your history: Identify all periods where Week 1 caused overpayment
- Calculate your refund: Work out exactly what you're owed
- Claim it back: Submit your claim and handle all communication
- Check other reliefs: While reviewing, we find additional refunds you might be entitled to
We can claim for up to four years. If you've been on Week 1 basis at any point since 2021, you may be owed significant refunds.
Other Reliefs You Might Be Missing
Week 1 overpayments are often just part of what you're owed. We also check for:
- Rent tax credit – up to €1,000/year
- Medical expenses – 20% relief
- Work expenses – for many professions
- Working from home – for remote workers
Been on Week 1 Basis?
Our experts will review your tax history and claim back what you've overpaid.
Start Your Free Review →No refund, no fee • Average refund €1,080 • TAIN: 77632V
Frequently Asked Questions
Is Week 1 basis the same as emergency tax?
They're related but different. Emergency tax applies when Revenue has no details for you—you get minimal credits. Week 1 basis means your correct credits apply but aren't cumulative. Both can result in overpayment.
Will the overpayment automatically sort itself out?
Not automatically. Revenue doesn't proactively refund Week 1 overpayments—you need to claim them back. That's where we help.
How far back can I claim?
Up to four years. If you were on Week 1 basis at any point since 2021, we can review those years and claim any overpayments.