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OMAD Calculator — One Meal A Day fasting window
Plan a OMAD (one meal a day) schedule from your last-meal time. OMAD is an aggressive protocol: you eat a single meal within a roughly 1-hour window and fast for about 23 hours, so this calculator models it as 23:1. Enter the time of your meal and it shows the eating and fasting windows as clock times, plus an approximate fasting-state timeline — a ~23-hour fast sits in the mild-ketosis band (16–24 hours), just short of the deeper-ketosis and autophagy range associated with 24 hours and beyond. Because the eating window is so short, OMAD makes it easy to under-eat protein and micronutrients, so it is not a beginner starting point. During the fast, stick to zero-calorie drinks — black coffee, plain water, unsweetened tea and electrolytes; cream, sugar, artificial sweeteners and BCAAs break it. OMAD is not safe for everyone: do not start without a clinician’s supervision if you have Type 1 diabetes or take insulin or sulfonylureas, if you are pregnant or breastfeeding, if you have a history of an eating disorder, or for children and adolescents. Lifestyle information, not medical advice.
OMAD → fast ~23h, eat within a ~1h window
- A ~23h fast lands in the approximate mild-ketosis band (16–24h)
- Short window → watch protein & micronutrients
Frequently asked questions
How many hours is OMAD fasting?
OMAD (one meal a day) is roughly a 23-hour fast with about a 1-hour eating window. This tool models it as a 23:1 protocol. It is one of the more extreme schedules, so most people build up through 16:8 and 18:6 first.
Does OMAD put you in ketosis?
A ~23-hour fast usually reaches mild ketosis (the approximate 16–24 hour band), just short of the deeper-ketosis and greater-autophagy range associated with 24+ hours. These timings are approximate and vary by person, diet and activity. Fasting ketosis is milder than ketogenic-diet ketosis. OMAD is not safe for everyone — check the contraindications first.