Most people guess at their calorie deficit, and that guess is usually wrong by several hundred calories. That gap explains why so many women eat “perfectly” for weeks and still don’t lose weight.
To figure out your calorie deficit for weight loss, start with your total daily energy expenditure (TDEE) — the calories your body burns each day. Eat roughly 300 to 500 calories below that number to lose about 0.5 to 1 pound per week, which is the range most research supports for sustainable loss. Your exact deficit depends on your age, height, weight, and activity level, so a one-size-fits-all number won’t work.
This article walks through the math step by step, explains why the standard formulas often miss the mark, and shows you how to adjust when the scale stalls. You’ll also learn why most people eat back their exercise calories without realizing it.
Key Points at a Glance
| Point | What It Means | Why It Matters |
|---|---|---|
| TDEE is your starting line | Your body burns a set number of calories daily just existing and moving | Eating below this number is the only way to create a deficit |
| 300–500 calorie deficit is typical | This range produces about 0.5–1 pound of loss per week | Smaller deficits preserve muscle and are easier to sustain |
| Activity level matters more than most think | Two women of the same size can have very different TDEEs | Using the wrong activity multiplier throws off your entire deficit |
| Adjustments are normal | Your body adapts as you lose weight | Rechecking your numbers every 10–15 pounds keeps progress moving |
| Exercise calories are often overestimated | Fitness trackers regularly overstate burn by 20–40% | Eating back all exercise calories usually kills the deficit |
What Is a Calorie Deficit, Exactly?
A calorie deficit simply means you consume fewer calories than your body burns in a day. Your body then pulls from stored fat to make up the difference. That process is the biological foundation of all weight loss, regardless of which diet plan you follow.
Your total daily energy expenditure has three parts: your resting metabolic rate (calories burned at complete rest), the thermic effect of food (calories burned digesting), and physical activity. Most women overestimate the activity part and underestimate the resting part, which skews the whole equation.
Practical note: I’ve worked with dozens of women who assumed they were “slow burners” when their activity multiplier was simply set too high. Choosing “moderately active” when you sit at a desk all day — even with a 30-minute workout — inflates your TDEE by 200–300 calories.
How to Figure Out Your Calorie Deficit Step by Step
Start by calculating your TDEE using the Mifflin-St Jeor equation, which research consistently shows is one of the most accurate formulas for most adults. For women, the equation is: 10 × weight in kg + 6.25 × height in cm − 5 × age in years − 161. That gives you your resting metabolic rate, not your total burn.
Next, multiply that resting number by an activity factor. Sedentary (little or no exercise) is 1.2, lightly active (1–3 days per week) is 1.375, moderately active (3–5 days) is 1.55, and very active (6–7 days) is 1.725. This step is where most people go wrong — be honest with yourself here, because overestimating activity is the single most common error.
Your final TDEE number is your maintenance calories. To figure out your deficit, subtract 300 to 500 calories from that figure. That gives you your daily target for weight loss of roughly 0.5 to 1 pound per week, which research indicates preserves more lean mass than aggressive cuts.
Practical note: A free TDEE calculator does this math instantly, which is worth using because the arithmetic trips people up. I always tell clients to recalculate after every 10 pounds lost — your TDEE drops as your weight drops, and eating last month’s target becomes maintenance.
Why the Scale Doesn’t Always Match Your Deficit
You can hit your calorie target perfectly and still see the scale stall for a week or two. Water retention from sodium, hormonal fluctuations, and changes in exercise all mask fat loss on the scale. Some studies suggest that women in particular retain more water during certain phases of their menstrual cycle, which can obscure real progress.
Instead of judging by daily weigh-ins, look at the trend over four weeks. If your average weight hasn’t moved after a month at your calculated deficit, your TDEE estimate is probably off — not your effort. Drop your intake by another 100–150 calories or increase your daily step count rather than making drastic cuts.
The evidence on weight loss plateaus is clear: your body adapts to lower intake and lower weight by reducing its energy expenditure. This is a normal metabolic response, not a sign of failure. Recalculating your TDEE with your current weight and adjusting your target is the evidence-based response.
Common Mistakes That Destroy Your Deficit
Underestimating portion sizes is the most frequent error. People regularly underestimate their intake by 30–50%, according to research on dietary recall. Using a food scale for at least two weeks gives you a reality check on what a real serving looks like.
Eating back exercise calories is the second biggest problem. Fitness trackers and gym machines overestimate calorie burn by 20–40%, meaning you’re often replacing more than you burned. Unless you’re training intensely for over an hour, most women don’t need to eat back exercise calories at all.
Liquid calories also slip through unnoticed. A daily latte with whole milk and syrup adds 300–400 calories, which can erase your entire deficit before lunch. Switching to black coffee or a smaller size is one of the simplest high-impact changes I recommend.
Practical note: When I help clients troubleshoot a stalled loss, the first three places I look are portion sizes, liquid calories, and exercise tracking. Fixing those three resolves the majority of cases without ever lowering their calorie target further.
How Low Is Too Low for a Calorie Deficit?
For women, eating below 1,200 calories per day is generally considered a clinical minimum that requires medical supervision. Very low-calorie diets below that threshold can cause muscle loss, nutrient deficiencies, and metabolic slowdown. Research consistently shows that aggressive deficits produce faster initial loss but higher rates of regain.
A moderate deficit of 300–500 calories is the sweet spot for most women because it’s sustainable over months. If your calculated target falls below 1,200 calories, that’s a signal that your activity level is very low or your weight is already in a healthy range — not that you should push lower.
Some evidence suggests that very low-calorie diets of 800–1,000 calories per day can be effective under medical supervision for certain individuals, but this is not appropriate for unsupervised use. If you’re considering anything below 1,200 calories, that conversation belongs with a doctor or registered dietitian.
Frequently Asked Questions
Related Articles
How do I find my TDEE without a calculator?
Use the Mifflin-St Jeor equation for women: 10 × weight in kg + 6.25 × height in cm − 5 × age − 161. Multiply that result by an activity factor between 1.2 and 1.725 depending on your exercise frequency.
Should I subtract 500 calories from my TDEE every day?
That depends on your weight and activity level. A 500-calorie deficit is appropriate for many women but can be too aggressive for petite or sedentary individuals.
Why am I not losing weight in a calorie deficit?
Your TDEE estimate is likely too high, your portion estimates are too low, or you’re retaining water. Check your intake with a food scale for two weeks and recalculate your numbers.
Can I eat back exercise calories and still lose weight?
Only if you’re training intensely for over an hour, because fitness trackers overestimate burn by 20–40%. For typical workouts, eating back those calories usually eliminates your deficit.
How often should I recalculate my calorie deficit?
Recalculate every 10–15 pounds lost or every 4–6 weeks. Your TDEE drops as your weight drops, so your target needs regular adjustment.
Once you know your numbers, try a free TDEE calculator to speed up the math. The formula is straightforward, but the calculator removes the arithmetic errors that throw people off.
Your calorie deficit is a starting point, not a prison sentence. The most effective target is the one you can actually follow for months — that’s the honest truth behind every successful weight loss story.
The TDEECAL Team writes about nutrition, metabolism, and fat loss the way we built our calculator, with real numbers and no hype. We dig into the research so you don’t have to guess.