Calorie deficit calculator
Enter your stats and pick how fast you want to lose. You get your maintenance calories, a daily target and, if you add a goal weight, the week you should reach it.
28% below maintenance. Losing 0.5 kg a week.
What a calorie deficit is and how it is calculated
A calorie deficit means you eat fewer calories than your body burns in a day. The shortfall has to come from somewhere, so the body draws on stored energy, mostly body fat, and you lose weight. No deficit, no fat loss, whatever the diet is called.
The calculator works in three steps: it estimates how much you burn at rest, scales that up for how active you are, then subtracts a deficit sized to the weekly rate you chose.
Step 1: resting energy (BMR)
Your basal metabolic rate is what you burn lying still for 24 hours: breathing, circulation, keeping organs running. It is the biggest slice of your daily burn, usually 60 to 70 percent. We estimate it with the Mifflin St Jeor equation, which uses weight, height, age and sex.
Step 2: maintenance calories (TDEE)
BMR is multiplied by an activity factor to give total daily energy expenditure, better known as maintenance calories. Eat that amount and your weight stays where it is. The factor runs from 1.2 for a desk job with no training up to 1.9 for athletes or physical work.
Step 3: the deficit
A kilogram of body fat stores roughly 7,700 kcal, so losing 0.5 kg a week needs a deficit of about 3,850 kcal a week, or 550 kcal a day. The calculator scales that for whichever rate you pick and subtracts it from maintenance. What is left is your daily target.
Why Mifflin St Jeor, and when another equation is better
Several equations estimate resting energy. They all use the same inputs and land in the same neighbourhood, but they were built on different populations and drift apart at the edges.
Mifflin St Jeor (used here)
Published in 1990 from a sample of 498 adults across a wide range of weights. In a 2005 systematic review by the American Dietetic Association it predicted measured metabolic rate within 10 percent for the largest share of people, both lean and obese. That is why it is the default in most clinical settings and in this calculator.
Harris Benedict
The original, from 1919, revised in 1984. It tends to overestimate by around 5 percent, especially in heavier people, because the sample was small and lean. Fine for a rough number, but there is no reason to prefer it now.
Katch McArdle
Uses lean body mass instead of total weight, so it needs a reliable body fat percentage. If you have one from a DEXA scan or a consistent caliper reading, it can be more accurate for very lean or very muscular people. If your body fat number is a guess, the error swamps the benefit. Use the body fat calculator first.
Cunningham
Also lean mass based, built on athletes. It runs higher than Katch McArdle and suits people training hard with a lot of muscle. Not a good fit for the general population.
Deficit sizes at a glance
The table shows what each rate of loss looks like in daily calories and what it is realistically good for. Percentages assume a 2,200 kcal maintenance; the calculator uses your own.
| Rate per week | Daily deficit | Weekly deficit | % of 2,200 kcal | Good for |
|---|---|---|---|---|
| 0.25 kg (0.5 lb) | 275 kcal | 1,925 kcal | 13% | Lean people, athletes in season, anyone who wants to keep strength |
| 0.5 kg (1 lb) | 550 kcal | 3,850 kcal | 25% | Most people. The rate guidelines recommend |
| 0.75 kg (1.5 lb) | 825 kcal | 5,775 kcal | 38% | Higher body fat, short push before tapering |
| 1 kg (2 lb) | 1,100 kcal | 7,700 kcal | 50% | Only with a lot of weight to lose and supervision |
How big should your deficit be?
For most people a deficit of 15 to 25 percent below maintenance is the sweet spot. It is large enough to see the scale move every week and small enough to keep training quality, sleep and mood intact.
Faster is possible but rarely better. Deficits above 1,000 kcal a day tend to cost muscle, wreck adherence and end in a rebound. If you have a lot of weight to lose you can run a larger deficit early on, when the body has more fat to draw on, then taper as you get leaner.
The calculator flags a target that drops below 1,200 kcal for women or 1,500 kcal for men. Below that it is hard to hit protein and micronutrient needs without supervision, and most people cannot sustain it anyway.
What to do with the number
Treat the target as a starting point, not a verdict. Every equation is an estimate and the activity factor is a guess, so the first two weeks are a calibration, not a test of willpower.
Track for two weeks, then adjust
Eat at the target, weigh yourself every morning and average each week. If the weekly average is falling at roughly the rate you chose, keep going. If it is flat, drop 100 to 150 kcal and check again in two weeks. If it is falling faster than planned, add a little back. Daily weight swings of a kilogram are water; only the weekly average means anything.
Protect protein
Protein matters more than any other macro in a deficit. Aim for 1.6 to 2.2 g per kg of body weight to hold on to muscle. Fill the rest with carbs around training and fats for the remainder. The macro calculator splits your target for you.
Recalculate as you lose
Maintenance falls as you get lighter, both because there is less of you to move and because the body adapts. Rerun the numbers every 5 kg or every 8 weeks so the deficit stays a deficit.
Hit a plateau? Three things to try
A plateau is two or more weeks where the weekly average has not moved. Before cutting calories further, check the basics: are you still weighing food, has training volume dropped, has a new block added water weight? If the tracking is honest, pick one of these.
Recalculate
Most plateaus are just the old target becoming maintenance. Put your new weight into the calculator and take the new number.
Take a diet break
One to two weeks at maintenance. It does not undo the fat loss, it lowers hunger and fatigue and it often restarts progress on the way back down. Useful every 8 to 12 weeks in a long cut.
Zigzag your calories
Keep the weekly total but move calories around: higher on training days, lower on rest days. The deficit is the same on average, adherence is usually better and the higher days keep hard sessions productive.
Common mistakes
Picking the wrong activity level. Most people overestimate. If you sit at a desk and train three times a week, you are lightly active, not moderately active. When in doubt pick the lower option and let the scale correct you.
Eating back exercise calories. The activity factor already includes your training. Adding what a watch says you burned counts it twice.
Not counting the small stuff. Cooking oil, milk in coffee and weekend drinks can add 300 to 500 kcal a day and quietly erase the deficit.
Judging by daily weight. Water, salt, carbs and the previous day's meal can move the scale a kilogram overnight. Compare weekly averages.
Never recalculating. A target set at 90 kg is maintenance at 80 kg.
How coaches use a calorie deficit calculator
For a personal trainer or online coach the calculator is the first five minutes of a nutrition plan, not the plan. The number sets a starting target; the coaching is in the check-ins that follow.
A workable routine: calculate the target at onboarding, set protein first, then review the weekly weight average and adherence every 7 days. Adjust in steps of 100 to 150 kcal and never more than once a fortnight, so you can tell what caused a change.
Scraler does that loop for you. Set a calorie and macro target per client, let them log meals in the app, and see the weekly average, adherence and check-in answers in one view instead of chasing screenshots. See nutrition coaching and client check-ins, or read how hybrid personal training packages nutrition with sessions.
Frequently asked questions
- How many calories should I eat to lose weight?
- Take your maintenance calories and subtract 15 to 25 percent. For someone maintaining on 2,400 kcal that is a target of roughly 1,800 to 2,050 kcal a day, which produces a loss of about 0.4 to 0.6 kg per week.
- Is a 500 calorie deficit enough?
- Yes, for most people. A 500 kcal daily deficit adds up to 3,500 kcal a week, which is close to half a kilogram of fat. It is the rate most guidelines recommend because it is sustainable and protects muscle.
- How do I calculate my calorie deficit by hand?
- Work out BMR with Mifflin St Jeor: 10 × weight in kg + 6.25 × height in cm − 5 × age, then + 5 for men or − 161 for women. Multiply by your activity factor (1.2 to 1.9) to get maintenance. Subtract 500 to 550 for 0.5 kg a week.
- What is the difference between TDEE and BMR?
- BMR is what you burn at complete rest. TDEE adds everyday movement, digestion and training on top, so it is the number you actually maintain your weight on. The deficit comes off TDEE, never off BMR.
- Why am I not losing weight in a calorie deficit?
- Usually because the deficit is smaller than it looks. Untracked foods, an activity level set too high or water retention from a new training block can all hide progress. Track everything for two weeks, weigh daily and compare weekly averages before changing anything.
- Should I eat back the calories I burn exercising?
- No. Your activity level already accounts for training. Eating back exercise calories on top of it double counts them and is the most common reason a deficit stops working.
- How long will it take to reach my goal weight?
- Divide the weight you want to lose by your weekly rate. Ten kilograms at 0.5 kg a week is about 20 weeks. Add a goal weight in the calculator and it gives you the date, but expect a few slower weeks along the way.
- Can I lose weight without counting calories?
- Yes, if whatever you do creates a deficit: smaller portions, more protein and vegetables, fewer liquid calories. Counting is just the most reliable way to know the deficit is really there, especially when progress stalls.
- Is a 1,200 calorie diet safe?
- For a small, sedentary woman it may be a normal deficit. For most adults it is too low to cover protein and micronutrient needs and is hard to sustain. The calculator warns below 1,200 kcal for women and 1,500 kcal for men; if your target lands there, pick a slower rate.
- Does the calculator work for muscle gain?
- It gives you maintenance, which is the starting point. For a lean bulk add 200 to 300 kcal on top of maintenance instead of subtracting. The bulking calorie calculator handles that directly.
- How accurate is this calculator?
- The Mifflin St Jeor equation lands within about 10 percent of measured metabolic rate for most adults. Use the number as a starting point and let two weeks of scale data fine tune it.
- Should I recalculate as I lose weight?
- Yes. Maintenance drops as you get lighter. Rerun the calculator every 5 kg lost or every 8 weeks, whichever comes first, and take the new target.
Sources
- Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990The BMR equation used here.
- Frankenfield D et al. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults. J Am Diet Assoc, 2005Systematic review that found Mifflin St Jeor the most accurate of the common equations.
- FAO/WHO/UNU. Human energy requirements. Report of a Joint Expert Consultation, 2004Physical activity level concept behind the activity multipliers; the 1.2 to 1.9 factors used here are the conventional Harris Benedict derived chart, not FAO PAL bands.
- Hall KD. What is the required energy deficit per unit weight loss? Int J Obes, 2008Why 7,700 kcal per kg is a reasonable planning figure, and where it breaks down.
- Helms ER et al. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr, 2014Protein intake of 1.6 to 2.2 g per kg and slower rates of loss for lean people.
Calories, macros, workouts and check-ins tracked per client, so the number you just calculated becomes a plan you can run. Free to try, no card needed.
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