Is There a 15-Hour Rule for HGV Drivers?
There's no standalone '15-hour rule' in the assimilated EU rules. The 15 hours comes from the 24-hour period minus a 9-hour reduced daily rest.
There is no standalone "15-hour rule" written into the assimilated EU drivers' hours rules. When drivers talk about a "15-hour rule," they usually mean the maximum length of the working day that's left once you take the shortest allowed daily rest — and that 15 hours is arithmetic that falls out of the rest rules, not a named limit in its own right.
Where the 15 hours comes from
The assimilated rules work in 24-hour periods. GOV.UK's assimilated drivers' hours guidance requires you to complete a daily rest within each 24-hour period — at least 11 hours, or a reduced 9 hours up to three times between weekly rests. If you take the minimum 9-hour rest, that leaves up to 15 hours of the 24-hour period for everything else: driving, other work, availability and breaks. So 24 minus 9 is 15. Take a regular 11-hour rest instead and the window is 24 minus 11, or 13 hours. Neither figure is a "rule" — each is just what's left after the rest.
Why calling it a rule is misleading
Treating 15 hours as a target you can always fill is a trap, because other limits bite well before it. Your daily driving is capped at 9 hours (10 twice a week). Your working time is limited by the 48-hour average, the 60-hour week and, if any of it falls between 00:00 and 04:00, a 10-hour night cap. And you still owe your 45-minute break within the day. A "15-hour day" only means you reduced your rest to 9 hours — it doesn't hand you 15 hours of free activity, and it costs you one of your three reductions.
Don't mix it up with GB domestic rules
The confusion is worse because the separate GB domestic rules — which apply to certain vehicles and journeys not caught by the assimilated rules — do set their own duty limits. Those are a different regime with different numbers, and they don't apply to most tachograph HGV work. If your work runs under the tacho and the assimilated rules, the "15 hours" is simply the spread left by a reduced daily rest, nothing more. Our which drivers' hours regime applies explains which regime applies to what.
What to do
Don't plan to "the 15-hour rule" — plan to your actual limits: daily and weekly driving, working time, night work, breaks and the rest you're going to take. If you reduce your daily rest to 9 hours, know that you've spent a reduction and that your day can at most be 15 hours, but usually much less once driving and working-time limits are applied. The free drivers' hours calculator applies all of these at once so you can see the real ceiling on your day, not a folk-rule. For operators, keeping drivers inside every genuine limit is what our per-vehicle plans are built to evidence.