Calorie deficit calculator

What is a calorie deficit?

A calorie deficit is what happens when you take in fewer calories than your body uses in a day. Your body makes up the gap by pulling from stored energy — primarily fat — and over time, that’s what weight loss actually is.

It’s the only mechanism proven to cause fat loss. No food, no supplement, no timing trick works without it. Every successful diet — keto, Mediterranean, high protein, intermittent fasting — works by producing a deficit, even when that’s not how the diet is marketed.

If you’ve searched how many calories should I eat to lose weight, the honest answer is: it depends on your body, your activity, and the pace you can actually stick to. That’s what the calculator above works out for you. The rest of this article covers how big a deficit to aim for, how to hit it consistently, and how to stop the number from drifting back up — without needing a spreadsheet.

How the calculator works (TDEE calculator + deficit in one)

This is a TDEE calculator and a calorie calculator for weight loss in the same tool: it works out your maintenance calories first, then takes the deficit you choose off the top. Your target comes from three steps. None of them are guesses.

1. Estimate your basal metabolic rate (BMR)

BMR is the energy you burn just keeping the lights on — breathing, circulating blood, maintaining body temperature. We use the Mifflin-St Jeor equation, which in a 2005 comparison against every major BMR formula had the smallest average error against indirect calorimetry¹.

Female: BMR = 10×kg + 6.25×cm − 5×age − 161
Male:   BMR = 10×kg + 6.25×cm − 5×age + 5

2. Multiply by your activity factor for TDEE

Total Daily Energy Expenditure (TDEE) is BMR plus everything you do on top — walking, fidgeting, training, typing. That total is your maintenance calories — what you’d eat to stay exactly where you are today. So the maintenance calories calculator step is just BMR multiplied by an activity factor:

Sedentary        × 1.2
Lightly active   × 1.375
Moderately       × 1.55
Very active      × 1.725
Extra active     × 1.9

3. Subtract a deficit for your pace

How much of a calorie deficit you actually need depends on the pace you’re comfortable with. A pound of fat stores roughly 3,500 kcal, so a 500 calorie deficit per day predicts around half a kilogram of loss per week — the most common “sweet spot” in the research. We cap the target at 1,200 kcal for women and 1,500 kcal for men — going below that for long stretches consistently fails, for reasons we cover in the next section.

Slow, moderate or fast: choosing your pace

Most people default to “fast”, assuming slower loss means better long-term results. The research is more nuanced. A 2014 Lancet trial compared a 12-week rapid weight loss programme against a 36-week gradual one and found no meaningful difference in weight regained 3 years later². So the case for a moderate pace isn’t really about keeping weight off longer — it’s about what happens to your body while you’re losing it.

Aggressive deficits tend to cost more muscle mass and produce steeper metabolic adaptation — your resting metabolism dropping further than body-weight change alone would predict, which makes maintenance harder once you stop⁵. Protein becomes more important the bigger the deficit: 1.2–1.6 g per kg of body weight is the range backed for general weight loss, with lean resistance-trained athletes benefiting from higher intakes up to around 2.2 g/kg⁴. A pace you can hold for 20 weeks without drifting into binges will always beat one you quit after three.

Rough guidance:

• Slow (−250 kcal, 0.25 kg/week) — if you have less than 10 kg to lose, you’re over 50, or previous faster attempts ended in a rebound.
• Moderate (−500 kcal, 0.5 kg/week) — the default for most adults with 10–25 kg to lose.
• Fast (−750 kcal, 0.75 kg/week) — only if you have more than 25 kg to lose, and only for 8–12 weeks at a time before a 2-week maintenance break.

5 common calorie deficit mistakes

Most people who say “the calorie deficit doesn’t work for me” have fallen into one of these. The deficit always works — the setup around it doesn’t.

1. Underestimating liquid calories. A cappuccino with oat milk, a glass of wine, and a smoothie can add 600–800 kcal you forgot to count. Liquids don’t trigger satiety the way food does³.
2. Eating too little protein. In a deficit, protein protects muscle mass and is the most satiating macronutrient gram for gram. Aim for 1.2–1.6 g per kg of body weight for general weight loss — higher (up to ~2.2 g/kg) if you’re lean and training with weights⁴. Our protein calculator gives you the exact number, and high-protein breakfasts make hitting it easier than you’d think.
3. Weekend drift. A 500 kcal weekday deficit plus a 1,500 kcal weekend surplus is a −1,000 net over 7 days — barely any deficit at all.
4. Overestimating exercise burn. Wearable devices and gym machines routinely overstate calorie burn by 20–40%. Don’t “earn” food from exercise; treat exercise as a separate lever.
5. Restarting the clock after every slip. One bad meal costs you a few hundred calories. Treating it like a reason to quit costs you weeks.

The “starvation mode” myth

Starvation mode — the idea that eating too little “shuts down” your metabolism so you stop losing weight — isn’t quite right, but it isn’t quite wrong either. Here’s what actually happens.

Very low-calorie diets (below 1,000–1,200 kcal) do cause metabolic adaptation: BMR drops by about 15% more than would be expected from weight loss alone, spontaneous activity falls (you fidget less, walk slower), and the hunger hormones ghrelin and leptin shift in ways that make eating more feel urgent⁵.

The scale doesn’t stop moving because of magic — it stops because the deficit you think you’re in has shrunk, and the pull toward overeating has grown. The fix isn’t to eat less. It’s to eat more at maintenance for a couple of weeks and then re-enter a moderate deficit.

How to sustain a deficit without counting every calorie

Counting calories works — but only a minority of people can do it for long enough to reach a goal. The more reliable approach is to structure what’s on your plate so the total naturally lands near your target.

Four habits do almost all the work:

• Protein at every meal. 25–40 g per meal, ideally from minimally processed sources (chicken, fish, tofu, Greek yoghurt, eggs, beans). Our protein calculator sets your daily target.
• Half the plate vegetables. Vegetables add volume and fibre with minimal calorie load — the mechanical lever that makes satiety easier.
• Decide on liquid calories once. Pick what’s worth it (your morning coffee, a weekend glass of wine). Remove the rest from the default.
• Keep the foods you love. A plan that bans your favourite meal is a plan with an expiry date.

This is the architecture Nutriguide plans are built on. The calculator gives you the number; the plan turns it into meals you actually want to eat.

When to recalculate your target

Your target isn’t permanent. As you lose weight, your body needs slightly fewer calories, so the same number that produced half a kilogram of loss three months ago produces none today. See our guide on breaking a weight loss plateau for the full diagnostic.

Recalculate:

• Every 3–4 kg of weight change.
• If your activity level shifts meaningfully (new job, injury, training block).
• After a plateau lasting more than 2–3 weeks of consistent eating.

If you’re already eating at the 1,200 / 1,500 floor and the scale has stopped, the answer isn’t to eat less — it’s to take a 10–14 day diet break at maintenance, then restart. That’s what long-term successful losers consistently do.