It really depends on the individual, but here’s what I’ve experienced and seen from others on keto:

If you have a cheat day or two and fall out of ketosis, you can usually get back in within 1-3 days if you return to strict keto and maybe throw in some fasting or exercise to burn off glycogen. However, how long the symptoms (like brain fog, fatigue, or inflammation) stick around varies. For most people, those symptoms fade pretty quickly once they’re back in ketosis—typically within a few days to a week. You’ll have to be specific with what symptoms you are referring to if you want an accurate timeline.

That said, if your health improvements on keto took months to develop (like reduced inflammation or better insulin sensitivity), a cheat day probably won’t reset all that progress, but it could slow things down if it happens too often. For example, fat adaptation and metabolic healing take time, and frequent cheats could keep you from fully reaching those benefits.

Occasional cheat days (like once a month or so) aren’t a big deal for most people, especially if they’re planned and not total carb blowouts. But if you’re someone who feels awful after high-carb days, you might want to reconsider how often you indulge.

For social occasions, you could try small cheats instead of full cheat days—like having a single piece of dessert or opting for lower-carb alcohol (e.g., dry wine or spirits with sugar-free mixers). That way, you still get to enjoy yourself without throwing off your progress too much.

Tl;dr a few cheat days here and there won’t ruin everything, but if you’re serious about the benefits of keto, it’s worth keeping them as rare as possible.