Is the 90-Hour Fortnight Fixed or Rolling Weeks?

The 90-hour fortnightly driving limit is measured over two consecutive fixed weeks — Monday-to-Sunday blocks — not a rolling 14-day window counted backwards from today. Each fixed week is tested against the fixed week immediately before it, so the "fortnight" is really any pair of consecutive fixed weeks.

Fixed weeks, paired up

The rules define a "week" as a fixed week running Monday 00:00 to Sunday 24:00. GOV.UK's assimilated drivers' hours guidance caps driving at 90 hours "in any 2 consecutive weeks." Because those weeks are fixed, the limit works on pairs of Monday-to-Sunday blocks: week 1 + week 2, then week 2 + week 3, and so on. It is not a sliding 14-day total that you recompute every day.

Why the distinction changes your planning

Under a rolling 14-day model you'd be juggling a total that shifts each day. Under the fixed-week model, the numbers settle at each Sunday-to-Monday boundary, which makes rota planning more predictable — but it also means every heavy week ties down both of its neighbours. A 56-hour week limits the week before it (they can total at most 90) and the week after it (same). So one big week can't simply be "paid back" in a fresh fortnight starting whenever you like — the pairing overlaps.

A worked example

Week 1: 40 hours. Week 2: 50 hours. Together that's 90 — right on the limit, legal. Now week 3: even a modest 45 hours pairs with week 2's 50 to make 95, a 5-hour breach of the 90-hour limit across weeks 2 and 3. Both weeks were inside the 56-hour weekly limit on their own, yet the pair is over. The infringement sits on the fortnight, which is exactly why drivers miss it — nothing looks wrong week by week.

What to do

When you check the fortnight, add the current fixed week to the one before it, then to the one after it, and keep both pairs at or under 90. Don't assume a new fortnight resets on a date of your choosing — the pairing rolls forward one fixed week at a time. The free drivers' hours calculator tracks consecutive fixed weeks so the 90-hour limit is applied correctly, and the daily, weekly and fortnightly driving limits are set out in one place. For operators, planning rotas that hold every pair of weeks inside 90 is part of what our per-vehicle plans are designed to keep visible.