Can you catch up on sleep on weekends? Only partly

Partly. A weekend lie-in pays back some of a short week's sleep, and you will usually feel better for it, but it doesn't fully undo a week of short nights, and a long one pushes your body clock later, which makes Sunday night and Monday morning harder. The steadier way to recover is to add sleep at the start of the night, keep your wake time close to normal, and fix the weeknights that caused the debt.

That is less satisfying than a Saturday morning in bed until eleven, but it is how you catch up without starting every week jet-lagged.

What is sleep debt?

Sleep debt is the gap between the sleep you need and the sleep you get, added up over several nights. The American Academy of Sleep Medicine recommends that adults get at least seven hours a night, and many people need more. If you need eight and get six on weeknights, you finish the week about ten hours short.

It helps to think of two kinds:

• Short-term debt: a couple of late nights before a deadline. You feel it, and a night or two of good sleep mostly sorts it out.
• Ongoing debt: short nights as the normal pattern, for weeks or months. People in this state often feel they have adjusted, but research on sleep restriction suggests that people tend to underrate how much short sleep is affecting them once it becomes routine.

A few signs you are carrying a debt: you can't get up without the alarm and the snooze button, you fade in the afternoon or in meetings, and you sleep much longer on days off than on workdays. That last gap is one of the clearest clues.

Does sleeping in on weekends help?

Some. If you have had a few short nights, extra sleep does help you recover, and you are likely to feel more alert and in a better mood after it. A lie-in is not useless.

But it has limits. In lab studies where volunteers slept short during the week and then slept as long as they liked at the weekend, the extra weekend sleep did not fully reverse the effects of the short nights, and some of those effects came back as soon as the short nights did. Studies that follow large groups of people over years have given mixed results, and they can only show links, not causes.

There is also a practical limit. Most people don't sleep as long at the weekend as the sums say they should. Ten hours short on Friday rarely becomes ten extra hours on Saturday and Sunday, because your body clock tends to wake you before then, and the rest of the debt carries into Monday.

Why a long lie-in can make Monday worse

Your body clock is set mainly by light, especially morning light. Sleep until 11 on Saturday and your first daylight arrives hours later than usual, so the clock drifts later. Stay up late on Saturday night as well and it drifts further. By Sunday night you aren't sleepy at your normal bedtime, you lie awake, and Monday's alarm arrives in what your body still thinks is the night.

Researchers call the gap between your body's preferred timing and the timing your week demands social jet lag. It feels much like flying east every weekend. Why a consistent bedtime matters covers the body clock side in more detail.

How to catch up on sleep without wrecking Monday

The aim is to get the extra sleep without moving the clock.

1. Go to bed earlier, not later. Add the extra sleep at the start of the night. An early Friday night does more for you than a late Saturday morning.
2. Keep your wake time close to normal. Many sleep experts suggest staying within about an hour of your weekday wake time. An extra hour is a treat, not a problem.
3. Get daylight soon after you wake. A walk, breakfast by a window, or coffee outside keeps the clock anchored.
4. Nap early, and briefly. If you are still tired, a 10 to 20 minute nap in the early afternoon is kinder to your clock than sleeping until noon. Naps for desk workers has the details.
5. Protect Sunday evening. Start winding down at your usual weekday time, so Sunday night goes the way Monday needs it to.

Here is the difference in practice, for someone who normally gets up at 7:

How long does it take to recover from sleep debt?

There is no fixed exchange rate between hours lost and nights needed to win them back. A couple of late nights before a deadline usually clear after a night or two of good sleep. A debt built over weeks or months takes longer, and it is paid back by changing the weeknights, not by any number of weekends. A fair sign you are back in credit: your weekend sleep stops being much longer than your weekday sleep.

A few small changes during the week do more than any lie-in.

• Move bedtime earlier in steps. Fifteen minutes earlier every few days is easier to keep than an hour all at once. Four steps and you have gained an hour a night.
• Find where the time goes. For most desk workers it is one of a few things: late work, a late coffee, or the hour of scrolling that feels like the only time that is yours. That last one has a name, revenge bedtime procrastination, and naming it helps.
• Keep the same times every day. A regular bedtime and wake time, weekends included, means your body is ready to sleep when you lie down, so more of your time in bed is spent asleep.
• Start winding down an hour before bed, with work closed and the lights low.

If you keep sensible hours and still need marathon weekends to function, or you feel exhausted however long you sleep, talk to a doctor. Loud snoring, waking up gasping, or sleep that never feels refreshing can point to problems that no lie-in will fix.

Guarding the weeknight bedtime

Notchpals has no idea whether you slept in; it doesn't track sleep at all. What it watches is the clock while you are at your Mac, and for desk workers a lot of weeknight debt starts right there. Choose Sleep as one of your crew's areas and set a bedtime, and a character comes down from the notch in the hour before it, then again if bedtime passes with you still working. Snooze, a sloth who would rather you were asleep too, keeps it soft:

SnoozeShhh... it's past bedtime... the emails can wait till morning...

Your bedtime is one setting, so the Saturday visit comes at the same time as Tuesday's. Here that is exactly what you want, because a regular bedtime does more for the debt than any lie-in. On weekend days, a Schedule character can add one more nudge: after 45 minutes at the Mac on a Saturday or Sunday, it drops by once to suggest the weekend might be better spent away from the desk.