No data yet? Start with a formula-based estimate — then come back in 2–3 weeks with real numbers for something much more accurate.
Whichever number you land on, it is a daily total — not a set of meal times. The rule that makes this workable on a rotating rota is simple: count calories across the whole twenty-four hours, not by the clock. It does not matter whether you eat between 8 and 18 or between 14 and 4. What matters is the total over the day as a whole. I have written more about why that matters so much on shifts in this guide.
Why there are two ways to get your number
A formula is a guess dressed up as precision. It knows your age, height and weight, but it does not know your actual metabolism, so treat it as a place to start, not an answer. The only way to know your real number is to eat a known amount for a few weeks and watch what your weight actually does.
I learned this the hard way. Years ago someone online who called himself a dietitian kept pushing my calories lower every time my weight loss slowed, until I was down to 1800 calories a day — and it turned out my real maintenance back then was probably closer to 3000–3500. The fat came off, but I was needlessly starving for months. I have written the full story here, including why your number is never the same as mine.
Your maintenance — your "zero" — is the number of calories where your weight holds steady. Eat above it and you gain. Eat below it and you lose. Find it, and dieting stops being guesswork.
This is a planning tool, not medical advice. It gives you a working number to test against your own results over a couple of weeks — it does not know your health history. If you have a medical condition, are pregnant, or anything here does not sit right for your situation, talk to a doctor or registered dietitian rather than trusting a website's number.
Know your number. Now find your window.
Shift work moves your sleep, and your sleep moves when you can actually eat. The sleep calculator works out a realistic window around your shift.
Open the Shift Sleep Calculator