Food logs, calculators and watches all estimate. Here's how to read the one signal that settles it, why it can hide for a week or two, and how to line up what you eat against what you burn.
The short version
8 sections · 5 min- A deficit means you burn more than you eat, added up over days and weeks, not meal by meal.
- The proof is a falling weekly-average weight. Day-to-day swings of a kilo or two are mostly water and food, not fat.
- As a rule of thumb, a 500 kcal daily deficit loses about 0.5 kg a week. It's an estimate, not a promise.
- Calories burned from a watch are estimates too. Use them for direction and let your weight trend correct them.
- Flat for three weeks while logging everything? Eat 100 to 200 kcal less a day, keep protein high, and check again.
What a calorie deficit actually is
Burning more than you eat, added up over days and weeks, not meals.
You're in a calorie when you eat less than you burn. Your body makes up the difference from stored energy, and over time that shows up as lost weight.
What you burn has two main parts: , the cost of simply being alive, and , everything you burn by moving. Digesting food adds a little more. Together they make your calories.
The balance
calories eaten − calories burneda deficit: you're losinga surplus: you're gainingKey point
It's a total, not a meal
A deficit is measured across days and weeks. One big dinner doesn't cancel a good week, and one light day doesn't make a cut.
The one test that settles it: your weight trend
If your weekly-average weight falls over two to three weeks, you're in a deficit.
Every other number in this guide is an estimate. Your weight over time isn't. It's the result of every calorie you ate and burned, so it's the one signal that can confirm a deficit. The trick is reading it without being fooled by daily noise.
- Weigh every morning, after the toilet and before you eat or drink.
- Keep it the same: same scale, same spot on the floor, same clothing (or none).
- Average each week. Your is the number that counts.
- Compare weeks, not days. A falling weekly average is a deficit. A single low morning is not.
| Week | Weekly average | Change |
|---|---|---|
| 1 | 82.4 kg | — |
| 2 | 82.1 kg | −0.3 kg |
| 3 | 81.8 kg | −0.3 kg |
Tip
Give it two to three weeks
The first week of a cut often looks dramatic because you lose water along with the it's stored with. Judge the trend from the weeks after, not the first one.
Why the scale can hide a deficit
Water moves faster than fat. For a week or two it can cover up real progress.
Fat loss is slow and steady. Changes in are fast and noisy. When the two move in opposite directions, the scale can sit still, or even rise, while you're losing fat underneath.
- A salty or high-carb day. Both pull extra water into your body, often a kilo or more by the next morning.
- A hard session, especially legs. Muscles hold extra water while they repair, for a few days.
- Food still on its way through. A big meal weighs something until it's digested.
- Hormonal cycles. Many women hold more water in the days before a period, which can hide a week of progress.
- Poor sleep and stress. Both can make your body hold more water for a while.
Key point
One flat week proves nothing
A flat week isn't evidence that you're not in a deficit. Three flat weeks of complete logging is.
Estimating your deficit from the numbers
Useful for setting a target and checking direction. Every input is an estimate.
You can estimate a deficit before the scale confirms it: take what you ate from your food log and what you burned from a calculator or a watch. It's a good way to set a target and to sense-check a week. Just remember both sides are estimates, and food logs tend to run low.
From a deficit to expected weight loss
7,700 kcal ≈ 1 kg of body fatdaily deficit × 7 ÷ 7,700 = kg lost500 × 7 ÷ 7,700 ≈ 0.45 kg a weekA starting point for what to expect. Your weight trend tells you what's actually happening.
- Early losses are mostly water. The first week or two drops more than the rule predicts, then it settles.
- Your burn shrinks as you get lighter. A smaller body burns a little less, and many people move a little less on a cut without noticing, so the same intake gives a smaller deficit over time.
- Body fat isn't pure fat. It also contains water and other tissue, which is part of why the number is an approximation.
None of this breaks the method. It's why you set a target from the estimate, then correct it from the trend.
What about calories burned from your watch?
Good for direction. Rough for exact numbers.
Resting energy
Mostly calculated from your age, sex, height and weight rather than measured. It's steady from day to day, and a reasonable estimate for most people.
Active energy
Estimated from your movement and heart rate. Studies that compare wearables with lab measurements find calorie estimates can be off by a wide margin, more than for steps or heart rate.
Workout calories
Usually already included in your active energy for the day. Adding them on top counts the same session twice.
- Watch the trend of your burn, not one day's number. Is this week more active than last?
- Don't eat back every workout calorie. If you do, keep it to a portion and let the scale tell you whether that works.
- Let your weight settle disagreements. If your watch says you're 600 kcal under every day and your weekly average hasn't moved in three weeks, the watch is the one that's wrong.
If you're not losing
Check the log before you cut the calories.
- Log everything for two weeks, weekends, drinks, cooking oil and sauces included. Most stalls are calories that never made it into the log.
- Weigh the calorie-dense foods a few times: oil, nut butter, cheese, rice and cereal. That's where eyeballing goes furthest wrong.
- Then adjust. If your weekly average is still flat, eat 100 to 200 kcal less a day, or add some daily steps, and give it another two to three weeks.
- Keep protein high so the weight you lose is mostly fat, not muscle. Our protein guide covers how much.
Watch out
Don't crash it
Very large deficits make it harder to keep muscle and harder to stick with the plan. Most people do well losing around 0.5 to 1% of their bodyweight a week.
If you have a medical condition or a history of disordered eating, talk to a doctor or registered dietitian before starting a deficit.
Wrap-up
How GainzMate shows your balance
What you ate and what you burned, side by side.
With Apple Health connected, Today shows Burned so far: your resting plus active energy for the day. Tap it to open Energy Balance, which shows what you've eaten against what you've burned, your deficit or surplus so far, and where the day should land if you eat to your target.
- Trends, not just today. Energy Balance in Insights charts your balance by day, week or month, with an estimated weight change for the period beside your Apple Health weigh-ins.
- Labelled honestly. Each figure shows whether it came from Apple Health or an estimate from your profile, and what you burn never changes your targets on its own.
- On your iPhone. Apple Health readings and your calorie balance stay on your device.
GainzMate is coming soon to iPhone. See Energy Balance on the features page.
Wrap-up
The bottom line
Key point
You're in a deficit if your weekly-average weight falls over two to three weeks of complete logging. Food logs, calculators and watches estimate the size of the gap; your weight trend proves it exists. When they disagree, believe the trend and adjust the numbers.