OMAD Calculator — One Meal a Day Weight Loss

Compressing a whole day's food into a single meal is the most aggressive of the common time-restricted patterns, and the arithmetic reflects it. With only one sitting, most people simply cannot fit their full maintenance calories in, so intake falls a long way. Reviews of intermittent fasting report intake dropping by 10–30% across the common protocols, with the shortest eating windows sitting at the top of that range (Varady et al., 2021); this calculator estimates roughly a 30–40% cut for a single daily meal. For the worked body — maintenance about 1,990 calories — that pushes intake down to roughly 1,290, a deficit near 700 a day. Notice how close 1,290 sits to the 1,200-calorie floor the tool warns about for women; a lighter person, or a slightly bigger appetite cut, tips below it, which is exactly the point at which OMAD stops being a good idea without guidance. The calculator flags that boundary for your own numbers.

A 700-calorie daily deficit is about 4,900 calories a week, which at roughly 7,700 calories per kilo of fat comes to about 0.63 kg — near 1.4 lb — every week for the worked body. That is close to double the pace of a 16:8 window, and it is where the temptation of OMAD lies. But faster is not the same as better. A pace this quick is more likely to cost muscle alongside fat, harder to sustain for more than a few weeks, and it leaves little margin above the safe intake floor. Steady loss you keep off beats rapid loss you rebound from. Confirm the maintenance the estimate rests on with the TDEE Calculator, then read your own weekly range above.

The One-Meal Problem

The hardest part of OMAD isn't the fasting — it's the eating. Landing an entire day of protein, fibre, vitamins and minerals in one meal is genuinely difficult, and most single meals fall short on protein in particular, which is the nutrient that protects muscle and controls hunger. If you run OMAD, make that one meal deliberately protein-forward and nutrient-dense rather than simply large. Plan the split with the Macro Calculator so the single window still covers your day.

There is no prize for the longest fast. If a single daily meal leaves you low on energy, preoccupied with food, or unable to hit your protein, a slightly longer eating window almost always serves you better. An 18:6 or 20:4 schedule keeps most of OMAD's deficit while giving you two meals to work with, which makes protein and nutrition far more achievable and the whole thing easier to hold week after week. The best schedule is the one you can keep — switch the dropdown in the calculator above to compare the projected loss from a gentler window before you commit.