Formula Used
BMR: Mifflin St Jeor equation. Male BMR = 10W + 6.25H - 5A + 5. Female BMR = 10W + 6.25H - 5A - 161.
TDEE: BMR × activity factor + planned exercise calories.
Thermic effect: protein calories × 0.25 + carb calories × 0.075 + fat calories × 0.025.
Net meal energy: OMAD meal calories - thermic effect estimate.
Daily energy gap: TDEE - net meal energy. It is then adjusted by adherence and adaptation.
Weekly fat change: daily energy gap × 7 ÷ calories per kg fat.
Projected scale change: total fat change + estimated first week water shift.
How To Use This Calculator
Enter age, sex, height, current weight, and goal weight first. Choose the correct unit for height and weight. Select your activity level. Add planned exercise calories if you track them separately.
Next, enter your OMAD meal calories and macro grams. The calculator uses macros to estimate thermic effect. Enter fasting hours for context. Add adherence if you do not follow OMAD every day.
Use adaptation when you want a cautious estimate. A higher value lowers the expected deficit. Set projection weeks and press calculate. Review the result above the form. Download the CSV or PDF for records.
OMAD Weight Loss From A Physics View
OMAD means one meal a day. The method changes meal timing. It does not cancel energy balance. Body mass changes when stored energy changes. This calculator uses that physics idea. It compares energy used with energy eaten.
Energy Balance Matters
Your body spends energy through resting metabolism, movement, exercise, digestion, and heat. The calculator estimates resting needs with a standard equation. It then multiplies by activity. Exercise calories are added separately. The final value is your estimated daily energy use.
The Meal Window
OMAD may make calorie control easier for some people. A short eating window can reduce snacks. It can also make protein and micronutrients harder to fit. That is why the form includes macros. Protein, carbs, and fats affect total meal energy. They also affect digestion energy.
Thermic Effect
Food digestion uses energy. Protein has the highest thermic effect. Carbs have a moderate effect. Fat has a smaller effect. The calculator subtracts an estimated thermic effect from the meal calories. This creates a net meal energy value.
Adherence And Adaptation
Real plans are not perfect. Social meals happen. Hunger changes. Training stress changes. The adherence field reduces the expected deficit. Metabolic adaptation reduces it again. This makes the projection more conservative.
Scale Weight
Scale weight is not pure fat. Water, sodium, glycogen, and bowel contents move daily. Early OMAD changes can show a fast scale drop. Some of that may be water. The water shift field keeps that separate from fat change.
Safer Planning
Use the result as an estimate. Do not chase extreme deficits. Very low calories can harm training, mood, sleep, and nutrition. Review progress weekly. Adjust calories slowly. Seek qualified guidance if you have medical concerns, pregnancy, diabetes, disordered eating history, or medication needs.
FAQs
What does this OMAD calculator estimate?
It estimates daily deficit, weekly fat change, projected scale weight, and time to goal. It uses energy balance, activity level, meal calories, macros, adherence, and adaptation.
Is OMAD required for weight loss?
No. OMAD is only one meal timing method. Weight loss mainly depends on a sustainable calorie deficit, enough protein, useful activity, and consistency.
Why does the calculator use activity factor?
Activity factor estimates energy burned beyond resting metabolism. A higher factor raises estimated TDEE. That can increase the calculated deficit when meal calories stay the same.
What is metabolic adaptation?
Metabolic adaptation is a cautious reduction in expected deficit. It represents lower energy use that may happen during prolonged dieting, reduced movement, or body weight loss.
Why include protein, carbs, and fat?
Macros estimate thermic effect. Protein uses more energy during digestion. Carbs use some. Fat uses less. The calculator uses these values to estimate net meal energy.
Can the result be exact?
No. It is an estimate. Real weight changes vary because of water, sodium, hormones, sleep, stress, training, tracking errors, and changes in daily movement.
What is first week water shift?
It is an estimated early scale change from water and glycogen. It is not counted as pure fat. You can set it to zero for a stricter projection.
Who should be careful with OMAD?
People with medical conditions, pregnancy, diabetes, medication needs, or eating disorder history should seek qualified guidance before using OMAD or aggressive calorie restriction.