OMAD Calculator
One meal a day means one plate has to carry the whole day. This works out what has to be on it — calories, a protein floor, a deficit that will not eat your muscle — and tells you when the answer is that it will not fit.
Before you start: OMAD is the most aggressive daily fasting protocol in common use, and the site it sits on says so. Do not run it while pregnant or breastfeeding, under 18, or with any history of an eating disorder, and do not run it on insulin or any other medicine that lowers blood sugar without your clinician changing the dose first. If you are new to fasting, this is the wrong place to start: build up through 16:8 and 18:6 over several weeks. Stop and eat if you feel faint, shaky or confused.
Step 1 of 2 · the safety check
Does any of this apply to you?
Tick everything that is true. The four in the first group stop this calculator outright — not as a scolding, but because none of them is a call a web page is fit to make. The rest do not stop it; they change what the numbers mean, and you will see why beside your result.
Nothing you tick is saved — not to a server, not to this browser. It never leaves the page.
Tick all that applyAny of these and the calculator stops
These do not stop it — they change what the numbers mean
Answer the screen to continue.
No numbers · this is the honest answer
This calculator will not give you an OMAD target.
You ticked something that puts one meal a day outside what a web page should be doing arithmetic for:
That is not a permanent no and it is not a judgement. It means the decision belongs to someone who can examine you, read your notes and change your medication — and none of that happens through a browser. Compressing a full day of food into one sitting moves blood sugar, blood pressure and the timing of every drug that has to be swallowed with a meal. When one of those is already being managed, OMAD is a change to the management.
If eating has been a difficult subject for you, there is a further reason to stop here. The feast-and-famine shape of one meal a day is the shape disordered eating already has, and a calculator that hands you a number to hit makes that worse rather than better.
Step 2 of 2 · your numbers
Who is eating this meal?
Your one meal
---
calories, eaten in one sitting
BMR
---
kcal at rest
Maintenance
---
kcal/day
Daily gap
---
kcal/day
Weekly change
---
kg/week
What has to be on the plate
Protein first, because it is the number that decides whether you lose fat or lose muscle. Fat is held at a quarter of the meal for hormone and vitamin absorption. Carbohydrate takes what is left.
Floor --- g (1.6 g/kg). Target --- g/kg for this goal.
For scale: ---. Vegetables and a starch carry the rest. The macro calculator splits the same total across two meals if you decide one is too many.
Your window
OMAD is a 23-hour fast with a one-hour window on the end of it.
If that hour looks brutal on paper, it probably is. The fasting window calculator builds the same schedule at 16:8, 18:6 or 20:4 around your sleep and work hours, and the meal window planner lays the meals inside it. Most of what people want from OMAD is available at 18:6 with two plates instead of one.
You ticked these on the way in
What they change about the numbers above
Nothing on this page was saved or sent anywhere. Reload and it is gone.
Where the numbers come from
The calorie number is standard energy-balance arithmetic and nothing more. Resting metabolic rate comes from the Mifflin-St Jeor equation, which is the equation validated as the most accurate of the common predictive formulas in non-obese and obese adults alike — and "most accurate" still means within 10 percent for roughly four people in five, so treat the output as a starting estimate rather than a measurement. That figure is multiplied by a standard activity factor to give maintenance calories, and the goal takes a percentage off it: 15, 20 or 25 percent for fat loss, nothing for maintenance, 10 percent on top for a lean gain. Weekly weight change is derived at roughly 7,700 calories per kilogram of body tissue, which is a linear rule of thumb that over-predicts loss the longer you run it, because a smaller body burns less. The protein floor is the one number here that is not arithmetic. It is 1.6 grams per kilogram of body weight, the point at which added protein stops producing further benefit for lean mass in the resistance-training meta-analysis, with 2.0 to 2.2 g/kg used while in a deficit, where the evidence favours the higher end. The calculator then applies the constraint OMAD adds and other calculators ignore: all of that has to land in one sitting. Protein synthesis responds to distribution as well as to total, and a dose split across two or three meals outperforms the same dose eaten once, so a protein target that grows past what one plate can plausibly hold is flagged rather than printed straight. Two floors are hard-coded and will not be crossed: intake never drops below 1,200 calories for women or 1,500 for men, and any target below your own estimated resting burn is marked as such. What the calculator cannot tell you is whether OMAD is a good idea for you. The one controlled trial of eating a full day of calories in a single meal found reduced fat mass alongside higher blood pressure, higher total and LDL cholesterol, and impaired morning glucose tolerance in healthy normal-weight adults — real trade-offs, in people with nothing wrong with them, at maintenance calories.
Sources
- 1. A new predictive equation for resting energy expenditure in healthy individuals — Mifflin et al., American Journal of Clinical Nutrition, 1990 (PubMed)
- 2. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review — Frankenfield et al., Journal of the American Dietetic Association, 2005 (PubMed)
- 3. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults — Morton et al., British Journal of Sports Medicine, 2018 (PubMed)
- 4. Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis — Areta et al., The Journal of Physiology, 2013 (PubMed)
- 5. A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults — Stote et al., American Journal of Clinical Nutrition, 2007 (PubMed)
- 6. Impact of reduced meal frequency without caloric restriction on glucose regulation in healthy, normal-weight middle-aged men and women — Carlson et al., Metabolism, 2007 (PubMed)
- 7. Body Weight Planner — National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health
Nothing on this site is medically reviewed — it cites its sources so you can check them. Read our editorial policy.