M1 Tax Code Explained: What It Means and How to Fix It (2025 Guide)
If you’ve just started a new job, switched employers, or noticed a strange code on your payslip, you might have seen something like 1257L M1 or 0T M1. It looks confusing—and sometimes it even means you’re paying more tax than expected. This is what’s known as the M1 tax code, often called a Month 1

