Calorie Deficit Calculator: How Much to Eat to Lose 1 lb a Week

The classic rule for fat loss: a deficit of 3,500 calories equals one pound. To lose one pound per week, eat 500 calories below your daily maintenance for seven days. The Calorie Calculator calibrates that maintenance number to you — your age, height, weight, sex, and activity level — because applying the “eat 1,800 calories” advice from a fitness influencer to your specific body is how most cuts fail. Here’s the actual math, why people get it wrong, and how to set up a deficit you can sustain through summer (and beyond) without hating your life.

Last updated: April 2026

The 3,500-Calorie Rule (And Where It’s Approximately Right)

One pound of body fat stores roughly 3,500 calories of energy. So if you create a daily deficit of 500 calories, you’re short 3,500 calories per week, which equals about one pound of fat loss per week. The math is approximate — bodies adapt, water weight fluctuates, and the 3,500-calorie figure is an average rather than a constant — but as a planning rule, it’s remarkably durable.

To set up a 1 lb/week cut you need two numbers:

1. Your maintenance calories — the amount you’d eat to keep your weight exactly stable, given your activity level. Also called TDEE (Total Daily Energy Expenditure).
2. Your target deficit — 500/day for 1 lb/week, 250/day for 0.5 lb/week, 1,000/day for 2 lb/week (rarely sustainable).

Maintenance minus deficit = your daily target. Hit it consistently, and the scale moves.

Why Generic Calorie Targets Fail

The biggest mistake in fat loss isn’t under-eating; it’s using someone else’s maintenance number. The fitness world is full of “eat 1,800 calories to lose weight” advice that ignores the 800-calorie spread between, say, a 5’3” sedentary 130-pound woman (maintenance ≈ 1,650) and a 6’1” active 200-pound man (maintenance ≈ 2,900).

If your maintenance is 1,650 and someone tells you to eat 1,800 to lose weight, you’ll gain. If your maintenance is 2,900 and you cut to 1,800, you’re in a 1,100-calorie deficit — aggressive, hard to sustain, and likely to kill your training and sleep within a few weeks.

The Calorie Calculator uses the Mifflin-St Jeor equation (the most accurate widely-used formula) to estimate your BMR (Basal Metabolic Rate — the calories you burn at rest), then multiplies by an activity factor to get TDEE. Inputs:

• Age, sex, height, weight
• Activity level: sedentary (desk job, no exercise), lightly active (light exercise 1–3 days/week), moderately active (3–5 days/week), very active (6–7 days/week), extra active (physical job + training)
• Goal: maintain, lose 0.5 lb/week, lose 1 lb/week, lose 2 lb/week, gain

The output is your daily calorie target plus a recommended macro split. Re-run the calculation every 10–15 pounds of weight change — your maintenance drops as you get smaller, so the same deficit gets shallower over time.

Sustainable Deficit Sizes (And When Each Makes Sense)

Small Deficit: 250 calories/day = 0.5 lb/week

For people close to their goal weight, women in the last few pounds of a cut, anyone wanting to maintain training quality. Sustainable for months at a time. Best for body recomposition (losing fat while gaining muscle).

Standard Deficit: 500 calories/day = 1 lb/week

The default for most people most of the time. Aggressive enough to see weekly progress on the scale but moderate enough to maintain workout intensity, sleep quality, and a normal social life. The recommended setting in the Calorie Calculator for sustained fat loss.

Aggressive Deficit: 750 calories/day = 1.5 lb/week

Reasonable for people with significant weight to lose (50+ lbs from goal), or for short cuts before a specific date (a wedding, photoshoot, beach trip). Difficult to sustain past 8–10 weeks. Hunger gets loud.

Crash Deficit: 1,000+ calories/day = 2+ lb/week

Almost universally unsustainable. Causes muscle loss, metabolic adaptation (your body lowers its calorie burn to match the low intake), poor sleep, irritability, and rebound eating once the diet ends. Avoid unless under medical supervision for medically necessary rapid weight loss.

Macros Matter as Much as Calories

You can hit your calorie target eating only Pop-Tarts and lose weight. You’ll also feel terrible, lose muscle, and gain it all back. Macronutrient split — protein, carbs, fat — is what determines whether your weight loss is fat loss or just “weight loss.”

Standard macro guidance for fat loss:

• Protein: 0.8–1.0 g per pound of bodyweight (or 1.6–2.2 g per kg). High protein preserves lean muscle while in a deficit and dramatically increases satiety.
• Fat: 0.3–0.4 g per pound (minimum 50–60g/day for hormone health). Below this and you risk hormonal disruption, especially for women.
• Carbs: the remainder. After protein and fat are set, the leftover calories become carbs. This is also where you have the most flexibility — lower carbs for keto/lower-carb approaches, higher carbs for athletes or hard training.

The Macro Calculator handles this split automatically and includes 5 diet presets (standard, keto, low-carb, high-protein, balanced) so you can see how the macros shift by approach. For deeper dives into protein distribution across meals, the Macros Per Meal guide explains why hitting your daily total isn’t enough — protein needs to be spread across the day for muscle protein synthesis.

The Summer Cut: 8–12 Weeks Out

If your goal is to lean out for summer (beach, pool, vacation, photo opportunity), the math gets practical. To lose 8 pounds: a 500-calorie daily deficit for 8 weeks. To lose 12 pounds: 12 weeks. Or a slightly larger deficit (700/day) for 8 weeks gets you about 11.

What works during a cut beyond the calorie math:

• Weigh yourself daily, average weekly. Daily weights bounce 2–5 pounds with water and digestion. The weekly average is the real signal. Drop the daily numbers into a spreadsheet or app and trust the trend, not the morning reading.
• Don’t cut training volume. Reducing both food and exercise simultaneously is how people lose muscle. Keep lifting heavy. Conditioning can be modulated.
• Sleep 7+ hours. Sleep deprivation crashes leptin (satiety) and spikes ghrelin (hunger). One bad week of sleep can derail weeks of disciplined eating.
• Hydrate aggressively. Dehydration is often misread as hunger. The Water Intake Calculator targets daily volume based on body weight and activity.
• Strategic refeeds. Once a week, eat at maintenance (no deficit) to restore glycogen, normalize hormones, and stay sane socially. The math still works because you’re in a weekly deficit even with one maintenance day.

What Goes Wrong (And How to Fix It)

The scale stops moving after week 3

Almost always one of three things: your maintenance estimate was too high to start (recalculate), your portions are creeping back up (track honestly for a week), or you’re losing fat but gaining water from training stress (look at clothes, not the scale).

Constant hunger

Increase protein. Add more fiber (vegetables, berries, oats). Drink more water. If hunger is still unmanageable after a week of these tweaks, your deficit is probably too aggressive — cut by 100–200 calories and see if it stabilizes.

Workouts feel awful

Pre-training carbs help. Take 30–60g of carbs in the 1–2 hours before lifting. Also reconsider if your deficit is too steep — chronic poor training is a sign your body is under-fueled.

Weight rebounds after the diet ends

The fix is not avoiding diets — it’s slowly increasing calories back to your new maintenance (which is lower because you’re lighter) over 2–4 weeks rather than immediately returning to your old eating pattern. The calculator can re-estimate your new maintenance once you’ve hit goal weight.

Run Your Numbers

Open the Calorie Calculator, enter your stats, and pick a goal. In ten seconds you’ll have a personalized daily target and macro split. Track to it for two weeks. Adjust based on what the scale and the mirror tell you. Sustainable fat loss is mostly arithmetic and patience — the calculator gives you the arithmetic; the patience is on you.