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Free FastingCalculator

OMAD Calculator

One meal a day: the simplest schedule to describe and the hardest to keep. Enter your meal time and see the full 23:1 cycle mapped out: free, instant, and judgment-free.

Fasting duration

OMAD is a scheduling decision, singular

Every other protocol asks two questions: when does the window open, when does it close. OMAD asks one: when do you eat? That single anchor defines the entire 24-hour cycle, which is why consistency matters more here than anywhere else: moving the meal from 6 PM to 9 PM quietly stretches one fast to 27 hours, and drifting earlier compresses the next cycle. The calculator above shows the exact cycle from your chosen hour, and thetimer records your actual meal times so drift is visible as data, not guilt.

The choice of hour is worth one deliberate decision. An evening meal (the most common) keeps you at the family table and makes social dinners the schedule rather than the exception. A midday meal suits people whose evenings run late or who sleep poorly after large meals. Either way, the strongest practical advice the scheduling math supports is: pick the hour your life already protects, because OMAD's one meal inherits every conflict that hour has.

The 23:1 cycle from a 6 PM meal

TimeState
6:00 PMWindow opens: the meal
7:00 PMWindow closes: fast begins
11:00 PM – 7:00 AMSleep (about a third of the fast)
7:00 AM – 12:00 PMMorning fasted stretch
12:00 PM – 6:00 PMAfternoon fasted stretch
6:00 PM next dayWindow reopens: cycle repeats

Enter your own meal hour above to shift the whole cycle. The calculator labels which events land today and which tomorrow, and can export all three boundaries to your calendar.

What we won't tell you about OMAD

Plenty of pages promise that hour 18 or 20 of an OMAD fast unlocks a named biological process on schedule, or convert "one meal a day" into a guaranteed weekly weight number. Human research doesn't support hour-precise claims like that, and we don't make them. What is factually true: an OMAD fast spans your entire sleep and nearly all waking hours; social eating outside the chosen hour is incompatible by definition; meeting nutritional needs in one meal takes deliberate effort; and studies of severe window compression report outcomes in the same family as other calorie-reducing approaches, not a separate category of results. If you want one-meal simplicity with slightly more slack, a20:4 window is the nearest neighbor and dramatically easier to live with.

Running OMAD with honest tooling

OMAD's all-or-nothing shape makes forgiving tools essential. Meal ran long? Edit the end time; the convention is a one-hour window, not a stopwatch. Ate a second time on a hard day? Log it; thehistory records an actual duration next to the target and moves on: no broken streak, no red marks, because the data is for you, not against you. Over weeks, your average cycle length tells you whether OMAD is your schedule or an aspiration; if the average keeps reading like 20:4, consider making that official. And because a 23-hour daily fast is genuinely demanding, thesafety guidanceis not boilerplate here: if any listed condition applies to you, professional advice comes before the first cycle, not after a rough week.

Common questions

What is OMAD?

OMAD (One Meal A Day) compresses all eating into a single daily meal, conventionally treated as a roughly 23-hour fast with a 1-hour eating window. Eat at 6 PM today, and your next meal is 6 PM tomorrow.

When is the best time for the OMAD meal?

There is no proven universal best hour. The practical considerations: an evening meal fits family and social dinners; a midday meal front-loads energy and leaves evenings fasted. Pick the hour your life already protects, then keep it consistent. The calculator shows the full cycle from any meal time.

Is OMAD safe?

OMAD is one of the most demanding common schedules, and it is genuinely difficult to cover nutritional needs in one meal. The safety note on this page applies with extra force: if you have any medical condition, take glucose-affecting medication, are pregnant or breastfeeding, are under 18, or have an eating-disorder history, do not start OMAD without professional guidance.

How much weight can you lose on OMAD?

We won't pretend to know. One meal a day makes large calorie deficits likely but not guaranteed: a single unrestricted meal can be substantial. Studies of severe window compression show results in the same family as other calorie-reducing approaches, driven by total intake. Any OMAD calculator promising specific pounds is inventing numbers.

Does OMAD produce faster results than 16:8?

Evidence does not show that extreme window compression reliably beats moderate schedules; comparisons keep finding that overall intake and adherence dominate. OMAD is a structural preference (one decision, one meal, zero ambiguity), not a certified shortcut.

What if my OMAD meal takes longer than an hour?

Nothing breaks. The one-hour window is a convention, not a physiological boundary. Use the custom duration option (for example 22 hours) if you routinely want a longer eating period.

Can I do OMAD a few days a week?

Yes. Some people run OMAD on selected days and 16:8 or 18:6 otherwise. Mixed weeks are legitimate schedules; the weekly planner supports per-day patterns and reports the true weekly total.

Is OMAD the same as a 24-hour fast?

Nearly. OMAD's 23:1 rhythm repeats daily around a fixed meal, while "24-hour fast" usually describes an occasional meal-to-meal fast (dinner to dinner). Arithmetically the calculator handles both: use the OMAD preset for the daily rhythm or a custom 24-hour duration for one-off fasts.

Do I need a special OMAD app or tracker?

No. OMAD needs exactly one boundary tracked, which the free timer here handles: start after your meal, let the countdown run to tomorrow's meal, and the history builds automatically on your device. No subscription tracker adds anything to a schedule this simple.

Can I drink coffee or water during the 23 fasting hours?

Water is generally considered compatible with fasting, and most OMAD practitioners include black coffee and plain tea. Anything with meaningful calories is, for scheduling purposes, a second meal. Whatever definition you choose, apply it consistently so your history stays comparable.

How does the timer handle an OMAD cycle?

Start it after your meal and it counts down the full 23 hours, then flips to a one-hour eating-window countdown at tomorrow's meal time. Meal ran long or moved? Edit the times; the cycle recalculates and the history stays honest.