Calorie Deficit Calculator

What a Calorie Deficit Actually Is

Your body needs a certain number of calories every day just to keep functioning: breathing, circulating blood, digesting food, and everything else that happens without you thinking about it. Add in the calories you burn through movement and exercise, and you get your Total Daily Energy Expenditure, or TDEE. Eat exactly that many calories and your weight stays flat. Eat less than that, and your body has to make up the shortfall from somewhere, which in practice means burning stored body fat (and, if the deficit is too aggressive or protein intake is too low, some muscle tissue as well).

That shortfall is the deficit. A 500-calorie daily deficit, kept up for a week, adds up to roughly 3,500 fewer calories than your body used, which is the commonly cited energy value of one pound of body fat. That is why a 500-calorie-a-day deficit is the standard recommendation for losing about one pound a week: it is not an arbitrary number, it comes directly from that energy math.

The tricky part is that TDEE is not a number printed on a package. It depends on your age, sex, height, current weight, and how physically active you are day to day, which is exactly why a calculator that walks through those variables individually tends to be far more accurate than a flat rule like "eat 1,500 calories a day."

How This Calculator Estimates Your Numbers

The calculator uses the Mifflin-St Jeor equation to estimate your Basal Metabolic Rate (BMR), the number of calories your body burns at complete rest. This equation, published in 1990 and validated repeatedly since, is the formula most dietitians and the Academy of Nutrition and Dietetics recommend over the older Harris-Benedict equation, because it tends to match measured energy expenditure more closely for most adults. See our how to calculate a calorie deficit guide for the full formula worked out by hand, step by step.

Once BMR is estimated, the calculator multiplies it by an activity factor to get your TDEE:

• Sedentary (little or no exercise): BMR x 1.2
• Lightly active (light exercise 1 to 3 days a week): BMR x 1.375
• Moderately active (moderate exercise 3 to 5 days a week): BMR x 1.55
• Very active (hard exercise 6 to 7 days a week): BMR x 1.725
• Extra active (very hard exercise plus a physically demanding job): BMR x 1.9

From there, the calculator subtracts a daily deficit sized to whichever weekly goal you pick (0.5, 1, 1.5, or 2 pounds a week, or the metric equivalents), and shows you the resulting daily calorie target. If that target would drop below a safe minimum (1,500 calories for men, 1,200 for women, figures widely cited by nutrition guidelines), the calculator caps it there instead and tells you so, rather than quietly recommending an intake that is too low to sustain.

Choosing a Weekly Weight-Loss Goal

Losing weight faster is not automatically better. A deficit of 1,000 calories a day sounds twice as effective as 500, but in practice it is much harder to sustain, tends to trigger more muscle loss alongside fat loss, and often leads to a rebound once willpower runs out. Most nutrition guidelines put a sustainable, healthy range at 0.5 to 2 pounds (about 0.25 to 1 kilogram) of weight loss per week, with 1 to 1.5 pounds a week being a common sweet spot for people with meaningful weight to lose.

Two exceptions matter. If you have less than about 15 to 20 pounds to lose, the slower end of that range (0.5 to 1 pound a week) is usually more realistic, since a smaller body has less metabolic "room" to run a large deficit without excessive hunger. If you have a larger amount to lose, the faster end (up to 2 pounds a week) is more achievable early on, and naturally slows down as your weight, and therefore your TDEE, decreases.

Worked Examples

Example 1: a moderately active woman. A 34-year-old woman, 5 ft 5 in (165 cm) tall, weighing 170 lb (77 kg), moderately active, has an estimated BMR of about 1,470 calories and a TDEE of about 2,279 calories. Choosing a 1 lb/week goal (a 500-calorie daily deficit) gives a target of about 1,779 calories a day. If her goal weight is 145 lb, the calculator estimates about 25 weeks, a little under 6 months, to get there at that pace.

Example 2: a sedentary man. A 45-year-old man, 5 ft 10 in (178 cm), 210 lb (95 kg), sedentary, has an estimated BMR of about 1,843 calories and a TDEE of about 2,211 calories. A 1.5 lb/week goal (a 750-calorie deficit) would put his raw target at about 1,461 calories, below the 1,500-calorie safe floor for men, so the calculator caps his target at 1,500 calories and flags it, suggesting a slightly smaller weekly goal (or some added activity to raise his TDEE) would let him hit the full 1.5 lb/week pace safely instead.

Example 3: a very active younger adult. A 24-year-old man, 6 ft (183 cm), 175 lb (79 kg), very active (training 6 to 7 days a week), has an estimated BMR of about 1,819 calories and a TDEE of about 3,137 calories, reflecting the large effect regular hard training has on daily energy needs. A 1 lb/week deficit still leaves him at about 2,637 calories a day, comfortably above the safe floor, illustrating why activity level matters just as much as body size when estimating a realistic target.

Common Mistakes That Stall Progress

Underestimating portions. Studies on self-reported food intake consistently find that people underestimate what they actually eat, sometimes by several hundred calories a day, simply from not weighing or measuring portions, forgetting cooking oil and condiments, or rounding down. A food scale for the first couple of weeks reveals more than most people expect.

Not adjusting as weight drops. TDEE falls as body weight falls, because a lighter body burns fewer calories at rest and during activity. A deficit that worked at 200 lb can quietly shrink to almost nothing by 170 lb if the calorie target is never recalculated. Recomputing every 10 to 15 pounds lost keeps the plan honest.

Confusing water weight with fat loss (or gain). Sodium intake, carbohydrate intake, hormonal cycles, and hydration status can shift the number on the scale by 2 to 5 pounds within a single day, with none of it representing actual fat gained or lost. Judging progress by a weekly or monthly average, rather than any single morning's reading, avoids a lot of unnecessary frustration.

Eating back exercise calories twice. The activity multipliers above already fold in a general estimate of daily movement and exercise. Separately adding back calories burned during a workout, on top of an activity level that already accounts for regular exercise, effectively cancels out part of the deficit without realizing it.

Going too low for too long. A very aggressive deficit can work for a few weeks, but sustained severe restriction increases the risk of muscle loss, nutrient deficiencies, and the kind of extreme hunger that makes a diet collapse entirely. The safe-minimum warning built into this calculator exists specifically to flag that situation before it happens. For more strategies on making a deficit stick day to day, see our weight loss tips guide.

When the Scale Stops Moving

Weight loss plateaus are normal, not a sign that something is broken. As TDEE gradually decreases with a lower body weight, a calorie target that produced a deficit a month ago can become close to maintenance without any change in eating habits. On top of that, the body makes small metabolic adjustments (sometimes called adaptive thermogenesis) during sustained dieting, modestly reducing energy expenditure beyond what the weight change alone would predict.

If progress stalls for more than 2 to 3 weeks despite consistent tracking, the most reliable fixes are: recompute your target at your current (lower) weight using this calculator, double-check that portions are still being measured accurately rather than creeping back up, and consider whether a diet break, a short period at maintenance calories, might help before continuing.

Safety and When to Talk to a Doctor

The estimates on this page are general guidance based on population-level formulas, not a personalized medical assessment. Individual metabolic rates can vary from the formula's prediction by a meaningful margin in either direction, and certain conditions (thyroid disorders, PCOS, some medications, pregnancy and breastfeeding) change calorie needs in ways a generic calculator cannot account for. Anyone with an existing health condition, a history of disordered eating, or who is considering a deficit larger than the ranges described above should talk to a doctor or registered dietitian before starting.