How big should my calorie deficit be?

A deficit of roughly 300–750 kcal/day below TDEE is generally considered a sustainable range for most healthy adults, producing weight loss of about 0.25–0.75 kg (0.5–1.5 lb) per week. Larger deficits can produce faster results short-term but are harder to sustain, carry a higher risk of muscle loss alongside fat loss, and are more likely to trigger rebound overeating. This calculator flags deficits it judges too aggressive relative to your stats.

Why has my weight loss stalled even though I am still in a deficit?

Several normal factors can cause this. First, as you lose weight your TDEE decreases (a smaller body burns fewer calories), so a deficit that worked at your starting weight can shrink toward maintenance as you get lighter — recalculating periodically helps. Second, water retention from stress, sodium intake, hormonal cycles, or recent exercise can mask fat loss on the scale for days or even a couple of weeks at a time. Third, people's adherence to a "diet" tends to loosen gradually without them noticing — extra bites, weekend drinks, and larger portions can quietly erode a deficit. A weekly weigh-in average, tracked over a month, gives a much clearer picture than any single day's number.

Is a 500-calorie deficit always right for everyone?

No — 500 kcal/day is a commonly cited round-number default because it maps to roughly 0.5 kg (1 lb) of weekly loss under the widely used 3,500 kcal-per-pound estimate, but it is not appropriate for everyone. For someone with a lower TDEE, a flat 500 kcal deficit could push daily intake dangerously low; for someone with a much higher TDEE, it may be an unnecessarily small deficit. Calculating your own deficit as a percentage or fixed amount relative to your individual TDEE, as this calculator does, is more appropriate than applying the same flat number to everyone.

What is the minimum number of calories I should eat?

General guidance commonly cited by dietitians suggests not going below roughly 1,200 kcal/day for most adult women or roughly 1,500 kcal/day for most adult men without direct medical supervision, as very low intakes make it difficult to meet essential nutrient needs and are harder to sustain. This calculator will flag a deficit that pushes your target below commonly recommended minimums. If a smaller body or lower TDEE means an appropriately sized deficit would fall below this range, a slower rate of loss (a smaller deficit) is generally the safer approach rather than pushing intake artificially low.

Can I use a calorie surplus calculator the same way?

Yes — this calculator supports both directions. Select "Gain weight" instead of "Lose weight" and it will calculate a calorie surplus using the same underlying logic, with a recommended, moderate surplus range (typically around 200–500 kcal/day above TDEE) designed to support gradual, largely lean gain rather than rapid weight gain that is more likely to be mostly fat.

Calorie Deficit Calculator – Calculate Calories for Weight Loss

How Calorie Deficits and Surpluses Actually Work

Weight change follows a simple energy-balance principle: eat consistently less than your body burns (a calorie deficit) and you tend to lose weight over time; eat consistently more than you burn (a calorie surplus) and you tend to gain. The complicating part is not the principle itself but estimating both sides of that equation accurately — how much you actually burn (your TDEE) and how much you actually eat — and choosing a deficit or surplus size that is both effective and sustainable.

This calculator starts from your TDEE (calculated the same way as our dedicated TDEE Calculator, using the Mifflin–St Jeor equation and an activity multiplier), then applies your chosen goal, target rate, and timeframe to produce a specific daily calorie number.

The 7,700 kcal-per-kg Rule

This calculator uses the widely cited estimate that roughly 7,700 kcal of cumulative deficit corresponds to about 1 kg of body weight lost (equivalently, roughly 3,500 kcal per pound) — an approximation based on the average energy density of human fat tissue, first popularised through research summarised by Max Wishnofsky in 1958 and still used as a practical rule of thumb in dietetics today. It is a simplification: it does not perfectly account for the fact that some early “weight lost” is water and glycogen rather than fat, that the ratio can shift somewhat as a diet progresses, or that the composition of weight lost (fat versus lean tissue) varies by individual, diet quality and exercise. It remains, however, a reasonably useful planning estimate for translating a calorie deficit into an expected rate of loss.

How to Read Your Result

The calculator gives you three key numbers: your estimated TDEE (maintenance calories), your daily calorie target (TDEE adjusted by your chosen deficit or surplus), and your projected weekly rate of change. Compare the projected rate against your actual weigh-ins over the following 2–3 weeks — if real-world results consistently differ from the projection, that is useful information about your real TDEE, and your target should be adjusted rather than treated as fixed forever.

Choosing a Safe, Sustainable Rate

Faster is not automatically better. Very aggressive deficits (more than roughly 1% of body weight lost per week for an extended period) are associated with a higher proportion of the weight lost coming from lean muscle rather than fat, greater difficulty maintaining adherence, disrupted hunger and fullness signals, and a higher likelihood of regaining the weight afterward. A moderate, sustainable deficit that you can actually stick to for months, paired with resistance training to help preserve muscle, consistently outperforms an aggressive short-term crash approach for most people’s long-term outcomes.

As a general guide:

Conservative (0.25–0.5% of body weight/week): easiest to sustain, minimal muscle loss risk, slower results.
Moderate (0.5–0.75% of body weight/week): a common, well-balanced default for most people with weight to lose.
Aggressive (0.75–1%+ of body weight/week): faster results but harder to sustain and carries a higher risk of muscle loss; generally more appropriate for shorter timeframes or people with more weight to lose, and best undertaken with attention to adequate protein intake and resistance training.

To put these percentages into concrete terms: for an 80 kg person, a conservative rate is roughly 0.2–0.4 kg/week, a moderate rate roughly 0.4–0.6 kg/week, and an aggressive rate roughly 0.6–0.8+ kg/week. For a 60 kg person, the same percentages translate to smaller absolute weekly losses — a reminder that “how much weight should I lose per week” does not have one universal answer independent of your own starting size.

Why the Calculator Flags Some Targets

If your selected deficit and timeframe would push your daily calorie target below a commonly recommended minimum (roughly 1,200 kcal/day for many women, 1,500 kcal/day for many men, though individual needs vary) or above a rate of loss generally considered aggressive, the calculator displays a warning rather than silently returning the number. This is not a hard block — it is a prompt to reconsider a more moderate, sustainable pace, or to speak with a healthcare professional or registered dietitian if a more aggressive approach is genuinely appropriate for your specific circumstances.

Common Reasons a Calorie Deficit “Stops Working”

People often describe a deficit that “used to work” and now doesn’t. The most common underlying reasons are: (1) TDEE has genuinely decreased as body weight has dropped, shrinking the real deficit at the same calorie intake; (2) portion sizes and incidental extras have crept up gradually without being logged; (3) activity level has unintentionally decreased (less walking, less NEAT) as part of feeling more tired on a sustained deficit; and (4) water retention is temporarily masking real fat loss. Recalculating TDEE periodically, tracking intake honestly (including drinks, sauces and “tastes”), and judging progress by weekly averages rather than single days all help identify which of these is actually happening.

Calorie Surpluses for Weight or Muscle Gain

The same calculator works in reverse for a gaining goal. A moderate surplus of roughly 200–500 kcal/day above TDEE is generally recommended for people aiming to build muscle or gain weight gradually, since it supports muscle growth without adding fat as quickly as a larger surplus would. Very large surpluses accelerate fat gain disproportionately to any extra muscle gained, especially beyond what a person’s current training experience and genetics can actually use for muscle building in a given week. Newer trainees generally have more capacity to build muscle quickly and can sometimes tolerate a slightly larger surplus productively, while more experienced trainees typically see diminishing returns from a larger surplus and are usually better served by a more conservative one to limit unnecessary fat gain alongside slower, harder-won muscle growth.

Rate of Weight Gain and What It Means

Similar to fat loss, the rate of weight gain matters for its composition. A very rapid rate of gain (more than roughly 0.5% of bodyweight per week sustained over time) is more likely to include a higher proportion of fat relative to muscle, since muscle can only be built at a limited biological rate regardless of how much surplus calorie intake is available. A slower, more moderate rate of gain — commonly cited guidance suggests roughly 0.25–0.5% of bodyweight per week for someone prioritising lean gain — tends to result in a more favourable ratio of muscle to fat gained over the same total weight increase, particularly when paired with a structured resistance-training programme and adequate protein intake.

Diet Breaks and Refeeds

For longer dieting phases (roughly 8 weeks or more), many nutrition coaches and some research support planned “diet breaks” — deliberate periods of one to two weeks eating at maintenance calories (TDEE) before resuming a deficit. The rationale is both psychological and physiological: a break can improve diet adherence and motivation for the following phase, may help reduce some of the hunger-hormone shifts associated with sustained restriction, and gives you a clean opportunity to recalculate TDEE at your current, lower body weight before continuing. This is different from a single “refeed day” (one day at a higher calorie intake, sometimes with a higher proportion of carbohydrate), which some people use for training performance or psychological relief but which has a much smaller and shorter-lived physiological effect than a genuine multi-week maintenance break.

Tracking Progress Beyond the Scale

Body weight is the most common way to track deficit progress, but it is also one of the noisiest, since it fluctuates day to day due to water retention, digestive contents, and hormonal cycles, independent of actual fat loss. Complementary ways to track progress include body measurements (waist, hips, chest — taken monthly, at the same time of day and in similar conditions for consistency), how clothes fit, progress photos (taken in consistent lighting and poses), and performance in the gym if you train. Using two or three of these together, rather than relying on the scale alone, tends to give a more complete and less discouraging picture of progress, particularly during periods where the scale itself seems stuck despite genuine fat loss happening.

Tools That Make Tracking Easier

If you plan to track your intake to hit a specific calorie deficit target, a free food-logging app (many are available for UK users, several with large branded and restaurant food databases) makes the process considerably easier than manual calculation, particularly for packaged foods with printed nutrition labels. A kitchen scale is a worthwhile inexpensive investment for anyone serious about accuracy — visual portion estimation is notoriously unreliable even for experienced trackers, and small underestimates across multiple meals a day can add up to a meaningful gap between your intended and actual deficit over the course of a week.

A Quick Recap

To summarise the full process: calculate your TDEE, choose a sustainable deficit or surplus size for your goal, use the 7,700 kcal-per-kg guide to set expectations for your rate of change, track consistently using weekly averages rather than daily numbers, and recalculate periodically as your weight shifts. Getting each of these steps right, rather than just picking an arbitrary daily number, is what separates a plan that reliably works over months from one that stalls within a few weeks.

Next Steps

Once you have a daily calorie target, use the Macro Calculator to split it into protein, carbohydrate and fat, or the Toby Carvery and Wetherspoons calculators to see how a specific restaurant meal fits into your daily budget.

Calorie Deficit Calculator