Calorie Deficit Calculator: How to Find Your Number
How do you calculate a calorie deficit?
A calorie deficit is the gap between the calories you burn each day (your Total Daily Energy Expenditure) and the calories you eat. To lose weight, you eat fewer calories than you burn. A deficit of 500 calories per day produces roughly 0.5 kg of fat loss per week for most people. Use the calculator below to find your specific daily calorie target based on your body stats and weight loss goal.
Table of Contents
Calorie Deficit Calculator
Calorie Deficit Calculator
What Is a Calorie Deficit?
A calorie deficit exists when you consume fewer calories than your body uses in a day. Your body requires a certain amount of energy, measured in kilocalories, to maintain its current weight. This is called your Total Daily Energy Expenditure, or TDEE. When you eat less than your TDEE, your body draws on stored energy, primarily body fat, to make up the difference. That is the mechanism behind fat loss.
One kilogram of body fat contains roughly 7,700 calories of stored energy. A sustained daily deficit of 500 calories produces a weekly shortfall of 3,500 calories, which translates to approximately 0.45 to 0.5 kg of fat loss per week under controlled conditions. This is why the 500-calorie daily deficit is the most commonly cited target for sustainable weight loss.
The critical word is sustained. A calorie deficit only produces results if it is maintained consistently over weeks and months. This is why the ease and accuracy of daily food tracking matters as much as knowing the right number.
How Does the Calculator Work?
The calculator uses the Mifflin-St Jeor equation, which is the most validated BMR formula in current use according to a 2005 review published in the Journal of the American Dietetic Association, to estimate your Basal Metabolic Rate.
The BMR formula is:
For men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age)
For women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age)
Your BMR is then multiplied by an activity factor to estimate your TDEE. The selected daily calorie deficit is subtracted from your TDEE to produce your daily calorie target.
The calculator applies a minimum floor of 1,500 kcal for men and 1,200 kcal for women to prevent the output from producing a target that is clinically unsafe. Targets below these thresholds require medical supervision.
What Is a Safe Calorie Deficit?
Research and clinical guidelines broadly support the following ranges:
Gentle deficit (250 kcal/day): Produces approximately 0.25 kg per week. Suited to people who are close to their goal weight, have a low TDEE due to low body weight or sedentary lifestyle, or who find larger deficits unsustainable. Very low risk of muscle loss or energy impact.
Recommended deficit (500 kcal/day): The standard recommendation from most clinical guidelines. Produces approximately 0.5 kg per week. Sustainable for most people without significant muscle loss or performance impact when protein intake is adequate.
Moderate deficit (750 kcal/day): Produces approximately 0.75 kg per week. Appropriate for people with more weight to lose. Higher risk of fatigue and muscle loss if protein intake is not prioritised.
Aggressive deficit (1,000 kcal/day): Produces approximately 1 kg per week. Generally recommended only for people with a high starting body weight under the supervision of a healthcare provider. Increases risk of nutrient deficiency, muscle loss, and metabolic adaptation.
A 2013 review published in the Journal of the Academy of Nutrition and Dietetics found that higher initial rates of weight loss tend to produce better long-term outcomes when protein intake is maintained, which challenges the widespread belief that slower is always better for sustainable results.
Why Does Your Calorie Deficit Change Over Time?
Your TDEE is not fixed. As you lose weight, your body requires fewer calories to maintain itself because there is less of it to maintain. A 90 kg person burns more calories at rest than the same person at 75 kg. This is why weight loss tends to slow as you approach your goal and why people often hit a plateau after several weeks of consistent progress.
Several other factors also affect your TDEE over time. Metabolic adaptation, where your body reduces non-exercise activity and metabolic rate in response to sustained energy restriction, can reduce actual expenditure below what a formula predicts. This is a well-documented phenomenon in weight loss research and is one of the reasons that recalculating your calorie target every four to six weeks, rather than using the same number indefinitely, produces better ongoing results.
Welling auto-adjusts your calorie target based on logged workouts and wearable data, which captures some of this variation in real time without requiring you to manually recalculate. Using a calorie deficit calculator alongside a tracking app that responds to your actual activity gives you both the starting number and the ongoing adjustment.
How Do You Track a Calorie Deficit Daily?
Knowing your target is the first step. Hitting it consistently every day is where most weight loss efforts succeed or fail.
The most common barriers to consistent daily tracking are the time it takes to log food manually, the difficulty of logging meals that are not in a database, and not knowing what to eat to stay within the target after a larger meal earlier in the day.
Welling addresses all three. It logs meals in 2.6 seconds on average from a photo, chat message, or voice note, with 95.6 percent food identification accuracy across 15,000 tested meals and a portion estimation error of 1.2 percent. When you ask it what to eat to stay within your remaining calorie budget for the day, the AI nutrition coach gives a specific answer based on your actual logged data.
This combination of a calculated target from the tool above and daily accurate logging in Welling is what turns a number on a page into consistent fat loss over weeks.
Start tracking your deficit free on Welling
You have the number. Now track it in seconds.
Welling logs meals from a photo, chat, or voice note in 2.6 seconds on average and shows your real-time progress against your calorie deficit target all day.
Frequently Asked Questions
What is a good calorie deficit for weight loss?
A deficit of 500 calories per day is the most widely recommended starting point for sustainable fat loss, producing approximately 0.5 kg per week. This is large enough to produce visible progress but small enough to maintain without significant muscle loss or energy impact when protein intake is adequate. Gentler deficits of 250 calories per day suit people closer to their goal weight or with lower starting TDEE.
Is a 500 calorie deficit too much?
For most adults with a TDEE above 1,800 calories, a 500-calorie deficit is not too aggressive and is broadly supported by clinical guidelines. It becomes problematic when the resulting daily calorie target falls below safe minimums (around 1,200 to 1,500 kcal depending on sex and body size), which is why the calculator above applies a floor. If a 500-calorie deficit puts you below 1,500 kcal as a man or 1,200 kcal as a woman, use a smaller deficit.
How accurate is a calorie deficit calculator?
The Mifflin-St Jeor equation used in this calculator has a margin of error of approximately 10 to 15 percent for individual TDEE estimates, based on research comparing predicted versus measured expenditure. This means your actual maintenance calories may be somewhat higher or lower than the calculator predicts. Treating the output as a starting point and adjusting based on real-world weight trend over two to three weeks produces more accurate individual targets than any formula alone.
What happens if I eat too few calories?
Eating significantly below your minimum safe intake leads to muscle loss, fatigue, nutrient deficiencies, and metabolic adaptation that makes further weight loss harder over time. Most clinical guidelines recommend a minimum of 1,200 calories per day for women and 1,500 for men as a floor for unsupervised dieting. The calculator above enforces these minimums in its output.
How do I know if my calorie deficit is working?
Track your body weight weekly, ideally at the same time of day under the same conditions, and average readings over each week to smooth out daily fluctuations. If your weekly average is decreasing by approximately the amount the deficit predicts, the numbers are working. If it is not, either the deficit is smaller than calculated (TDEE overestimated, intake underreported) or metabolic adaptation has reduced expenditure below the formula's prediction.
Does the calorie deficit calculator work for everyone?
The Mifflin-St Jeor formula works reasonably well for most adults but has limitations for very muscular or very lean individuals, where BMR is typically underestimated, and for older adults with lower muscle mass, where it may overestimate. Athletes, people with specific medical conditions, and anyone on medication that affects metabolism should treat the output as a starting estimate and adjust based on real-world tracking results.
References
Mifflin, M. D., et al. (1990). A New Predictive Equation for Resting Energy Expenditure in Healthy Individuals. American Journal of Clinical Nutrition, 51(2), 241-247. https://pubmed.ncbi.nlm.nih.gov/2305711/
Frankenfield, D., Roth-Yousey, L., & Compher, C. (2005). Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults. Journal of the American Dietetic Association, 105(5), 775-789. https://pubmed.ncbi.nlm.nih.gov/15883556/
Hall, K. D., & Guo, J. (2017). Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition. Gastroenterology, 152(7), 1718-1727. https://pubmed.ncbi.nlm.nih.gov/28193517/
Johansson, K., et al. (2014). Effects of Anti-obesity Drugs, Diet, and Exercise on Weight-Loss Maintenance After a Very-Low-Calorie Diet or Low-Calorie Diet. American Journal of Clinical Nutrition, 99(1), 14-23. https://pubmed.ncbi.nlm.nih.gov/24172304/
Tremblay, A., & Chaput, J. P. (2012). Adaptive Thermogenesis Can Make a Difference in the Ability of Obese Individuals to Lose Body Weight. International Journal of Obesity, 36(6), 771-776. https://pubmed.ncbi.nlm.nih.gov/22027950/
Burke, L. E., et al. (2011). Self-Monitoring in Weight Loss: A Systematic Review of the Literature. Journal of the American Dietetic Association, 111(1), 92-102. https://pubmed.ncbi.nlm.nih.gov/21185970/
