Calorie Deficit Explained: How Much Should You Eat to Lose Weight?

Quick summary

You lose weight when you consistently take in fewer calories than your body uses.
A deficit of about 500 calories a day is a common, sustainable starting point.
Estimate your needs with a formula or the NIH Body Weight Planner, then adjust based on real results.
Weight loss slows over time, so the “3,500 calories = 1 lb” rule overestimates long-term results.

Every successful diet, whether it’s low-carb, Mediterranean or plant-based, works by creating a calorie deficit. Understanding how it works helps you choose an approach you can stick with.

What is a calorie deficit?

Your body burns energy all day: to keep your heart beating and organs working (your basal metabolic rate, or BMR), to digest food, and to move. Together, that’s your total daily energy expenditure (TDEE). When you eat fewer calories than your TDEE, your body makes up the difference from stored energy, mostly fat.

Step 1: Estimate your daily calorie needs

A widely used estimate of BMR is the Mifflin–St Jeor equation:

Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

Then multiply by an activity factor: about 1.2 if you’re mostly sitting, 1.375 if lightly active, 1.55 if moderately active, and 1.725 if very active.

Example: a 40-year-old woman, 165 cm tall, 85 kg, lightly active: BMR = 850 + 1,031 − 200 − 161 = 1,520 calories. TDEE ≈ 1,520 × 1.375 ≈ 2,090 calories a day.

Prefer not to do math? The free NIH Body Weight Planner does it for you and also models how your weight changes over time.

Step 2: Choose a moderate deficit

Subtracting about 500 calories a day from your TDEE is a common starting point. In the example above, that means eating about 1,600 calories a day. Early on, this usually produces roughly 1 lb (0.5 kg) of weight loss per week, in line with the safe rate recommended by health agencies.

Many experts suggest not going below about 1,200 calories a day for women or 1,500 for men without medical supervision, because it becomes hard to meet your nutrient needs.

Why the “3,500 calorie rule” is only a rough guide

You may have heard that cutting 3,500 calories equals one pound of fat. It’s a useful rule of thumb for the first weeks, but research by Kevin Hall and colleagues at the NIH showed that it overestimates long-term weight loss. As you get lighter, your body needs fewer calories, so the same intake produces a smaller deficit. That’s one reason weight loss slows and plateaus happen. It’s normal, not failure.

Step 3: Make the deficit easy to live with

Fill up on low-calorie, high-volume foods like vegetables, fruit, broth-based soups and salads. See Add Veggies to Everything.
Get enough protein. It keeps you fuller and helps protect muscle. See Choose Lean Proteins.
Watch liquid calories. Sodas, sweet coffee drinks and juice add up fast. See Limit Added Sugars.
Move more. Walking, taking the stairs and strength training increase the energy you burn.
Sleep 7+ hours. Short sleep is linked with increased hunger and cravings.

Step 4: Track, then adjust

Formulas are estimates. Track your weekly average weight for 2–3 weeks. If you’re losing about 0.5–1% of your body weight per week, keep going. If nothing is changing, reduce intake by 100–200 calories or add more activity. If you’re losing much faster or feel exhausted, eat a bit more.

The bottom line

A calorie deficit isn’t a diet; it’s the principle behind every diet. Choose a moderate deficit, build meals around protein and vegetables, and adjust based on your real results.

Sources

This article is for general education and isn’t medical advice. Talk to your doctor or a registered dietitian before changing your diet or exercise routine, especially if you have a health condition, are pregnant or take medication. See our Medical Disclaimer.