National Insurance
What it really means
A separate payment taken from your wages (as well as income tax) that builds up your right to the State Pension and some benefits. Often written NI or NIC. Employees pay it automatically through PAYE.
Context, tips & common mistakes
Unlike income tax, NI is worked out per payday, not per year — so an unusually big single payslip (a bonus month, lots of overtime) attracts more NI and there is generally no year-end refund the way there is for overpaid income tax. What you get in return is a contribution record, and that record matters long-term: your eventual State Pension depends on building up enough qualifying years, and gaps show up decades later. Check your record for free in the personal tax account — years spent studying or on low hours may not count, and GOV.UK explains when filling gaps voluntarily is worthwhile.
One scam to know: cold callers claiming your 'National Insurance number has been used in fraud' and threatening arrest are always fake; HMRC and the police do not make such calls. Hang up without pressing any buttons.