Calorie Deficit Calculator

How the calorie deficit calculator works

Three numbers do most of the work. Your basal metabolic rate (BMR) is what your body burns at rest. We calculate it with the Mifflin-St Jeor equation, which lands within roughly 10% of indirect calorimetry and beats the other common BMR formulas for accuracy. Multiply that by an activity factor (1.2 for sedentary, up to 1.9 for extra active) and you get total daily energy expenditure, or TDEE. That is the number of calories you burn on a typical day.

The daily calorie target then takes your weekly weight-change goal, converts it to calories with the 3,500-cal-per-pound rule of thumb, and adds or subtracts the right amount from your TDEE. Macros come last. Protein is anchored to body weight (1.0 g/lb standard, 1.2 g/lb if you want more muscle protection), fat sits at 25% of calories (well inside the 20 to 35% IOM range), and carbs fill in whatever is left.

How to use a calorie deficit during your 75-day challenge

A 500 cal/day deficit fits a 75-day challenge cleanly. That is about 1 lb/wk of loss, or roughly 10 lb across the full 75 days, with enough fuel left over for two daily workouts and proper recovery. Anything past 1,000 cal/day starts cutting into recovery, sleep quality, and that second workout. Progress usually flatlines before day 75.

Recalculate every two to three weeks. As you get smaller your TDEE drops, so the same intake turns into a smaller deficit over time. Pair this calculator with the 75-day challenge calculator for your timeline, and the water intake calculator for daily hydration. If you want a free way to log your daily streak alongside your nutrition, Reset75 handles checklists, photos, and stats with no account required.

Common mistakes that stall progress

Eating back exercise calories. Most fitness trackers overstate calorie burn by 20 to 50%. Trust your TDEE multiplier, not the watch on your wrist.

Weekend creep. A clean Monday-to-Friday paired with an unmeasured weekend will often wipe out the entire week. Track every day, or set a small protein-forward weekend default you can fall back on.

Dropping protein. Cutting calories by trimming protein costs you muscle and slows your metabolism. Hit the protein number first. Then pull from carbs or fat.

Going below the safety floor. Aggressive deficits past 1,000 cal/day usually backfire. Slower is sustainable, and sustainable is what wins inside 75 days.

Ignoring sleep and stress. Both push hunger hormones up and pull NEAT down. A 7- to 8-hour night beats another 200 cal cut.

Macros: protein, carbs, and fat in a deficit

Protein is the only macro tied to body weight rather than total calories, because the goal during a cut is to keep the muscle you have. One gram per pound is the well-supported starting point. Bump it to 1.2 g/lb if you are leaner or training hard. Fat sits at 25% of total calories, which falls inside the IOM acceptable range of 20 to 35% and leaves room for hormone health and satiety. Carbs take whatever is left, which is usually plenty for training fuel unless your daily target is very low.

Low-carb and high-fat splits work too. For most people running a 75-day challenge though, the protein-first setup with moderate fat and carbs is the easiest to stick with and the kindest to two-a-day workouts. Run the defaults for two weeks, then adjust based on energy in the gym and how full you feel between meals.