Calorie deficit but not losing weight? 9 reasons and what to do

You’ve worked out your calories, you’re sticking to them, and the scale won’t budge. It’s one of the most frustrating parts of losing weight, and it’s very common. The good news is that the reasons are well studied, and most of them are fixable with better information rather than more willpower.

A quick note first: everything below is about healthy adults. If you’re pregnant or breastfeeding, under 18, have a history of disordered eating, or have a medical condition, work out your plan with a doctor or registered dietitian. Calorix never sets a deficit for anyone under 18.

1. You’re eating more than your log says

This is the most common reason by far, and it’s not a character flaw: almost everyone under-counts. In a classic 1992 study, 10 people who said they couldn’t lose weight on under 1,200 calories a day were measured precisely for two weeks. Their metabolism was normal, within 5% of predicted, but they under-reported what they ate by 47% on average and over-reported their activity by 51%.

That was a small group of people with a long history of dieting, but under-reporting shows up in everyone. In the OPEN study of 484 adults, checked against objective biomarkers, 24-hour food recalls under-reported energy by 12 to 20%.

2. Hidden calories: oils, drinks and extras

The usual culprits are things that don’t feel like food: the oil in the pan, butter on toast, dressing, sauces, a latte, juice, a glass of wine, bites while cooking. Fat is dense, so a little goes a long way: one tablespoon of olive oil is 119 calories (USDA FoodData Central). Two forgotten tablespoons a day add up to about 1,700 calories a week.

3. Your photo or label estimates run low

If you log by photo, your log may be running low without you knowing. In a preliminary 2026 NIH study, the photo features of four popular apps under-counted weighed meals by 252 to 345 calories on average, about a third, mostly from fat. Barcodes and labels are better for packaged food, though even labels aren’t exact. More in How accurate are AI calorie apps?

4. Weekends undo the weekdays

A year-long study of adults following a calorie-restriction or exercise plan found that, before the plan, people gained weight on weekend days but not weekdays, because they ate more on Saturdays and moved less on Sundays. During the plan, the calorie-restriction group stopped losing weight on weekends, which “helps to explain the slower-than-expected rate of weight loss.” If you only log carefully from Monday to Friday, your weekly deficit may be much smaller than your daily one.

5. Your target was set too high

Calorie targets start from an estimate of how much energy you use, and estimates can be off. The equations used by calculators and apps, including the Mifflin-St Jeor equation behind our TDEE calculator, predict an average for people like you; your real number can be higher or lower. Activity is the biggest source of error: people tend to pick a more active level than their week really is, as the 1992 study above found. If you’re not sure, choose the lower activity level and adjust from real results.

6. Water is hiding the fat loss

Body weight moves for reasons that have nothing to do with fat:

• Glycogen and water. Your muscles and liver store carbohydrate as glycogen, and each gram is stored with at least 3 grams of water (Fernández-Elías, 2015; Kreitzman, 1992). A carb-heavy day can add water weight overnight, and the fast drop in the first week of a diet is partly water too.
• Day of the week. In a study of 1,421 people with smart scales, weight swung about 0.35% within a normal week: highest on Monday, lowest on Friday. For a 90 kg (200 lb) person, that’s about 0.3 kg (0.7 lb) of noise.
• The menstrual cycle. In a 2023 study of 42 women, weight was about 0.45 kg (1 lb) higher during menstruation than in the first week of the cycle, mostly extracellular water. Compare the same phase of your cycle month to month.

7. It hasn’t been long enough, and the 3,500-calorie rule overpromises

The old rule that 3,500 calories equals a pound of fat predicts steady, linear weight loss. Researchers at the NIH showed it overestimates, because it “ignores dynamic physiological adaptations” as your body changes (Hall et al., The Lancet, 2011). Their model suggests weight responds slowly to a change in intake: about half of the eventual change takes around a year. The NIH Body Weight Planner uses this kind of model to give more realistic timelines.

8. You burn less as you lose weight

A smaller body needs less energy, and the body also adapts. When people keep off 10% or more of their weight, their daily energy use falls by about 20 to 25%, and 10 to 15% of that is more than the change in body size alone would predict, or roughly 300 to 400 fewer calories a day (Rosenbaum and Leibel, 2010). A target that was a deficit at the start can become maintenance later. Recalculate your target after every few kilos lost.

Sleep matters in a related way. In a small 2010 study, people on the same calorie deficit lost the same weight with 5.5 or 8.5 hours in bed, but with short sleep they lost less than half as much fat (0.6 vs 1.4 kg), more muscle and felt hungrier.

9. A medical condition or a medicine

Sometimes the cause is medical. An underactive thyroid can cause weight gain, though the NIDDK notes that weight gain and tiredness are common and “do not necessarily mean you have a thyroid problem” (NIDDK). Cushing’s syndrome (NIDDK) and polycystic ovary syndrome, which can cause “trouble losing weight, especially around the waist” (NICHD), are others. Some medicines can cause weight gain too, including birth control pills, corticosteroids and some medicines for depression, bipolar disorder, schizophrenia and diabetes (MedlinePlus; systematic review). Never stop a medicine without talking to your doctor.

A two-week check

Before changing your plan, find out which of the reasons above applies. For two weeks:

1. Log everything, every day, weekends included: drinks, oils, sauces, bites and tastes.
2. Weigh the foods you eat most a few times, such as your usual bowl of cereal, scoop of rice or pour of oil, to calibrate your estimates.
3. Use barcodes and labels for packaged food, and check and correct photo estimates, adding the cooking fat.
4. Weigh yourself at the same time each morning and look at the weekly average, not single days. A review of 17 studies linked regular self-weighing with more weight loss and no harm to mood (Zheng, 2015); if it makes you anxious, weigh weekly.
5. Compare week one with week two. If the average is falling slowly, you’re on track: the CDC notes that people who lose about 1 to 2 pounds a week “are more likely to keep the weight off than people who lose weight quicker” (CDC). If it isn’t moving, recalculate your target with the calorie deficit calculator using a lower activity level.

If you’ve logged carefully for several weeks and nothing changes, or you’re gaining weight without explanation, see your doctor.

How Calorix helps you find the missing calories

Calorix is built around the problems above. Photo estimates come back as a list of ingredients with grams and a confidence badge, so you can spot what’s off and add the oil the camera missed, or tell Fix with AI what to change. Barcodes and nutrition labels cover packaged food, and voice and text logging make the small extras quick to add. Your weight trend shows the weekly direction instead of daily noise, and your target is set with a pace capped at 1% of body weight a week and never below 1,200 calories a day for women or 1,500 for men. See how Calorix sets your calorie target.