Is the 3,500-calories-per-pound rule accurate?

It is a widely used approximation, not a law of physics. It can provide a reasonable order-of-magnitude estimate for some people, especially in the early stages of weight loss, but individual responses vary and metabolism adapts over time.

Should I use a very large calorie deficit to lose weight faster?

Bigger deficits come with trade-offs: increased hunger, lower energy, potential loss of lean mass, and higher risk of rebound if the plan is too aggressive. Many people do better with a moderate deficit they can maintain alongside resistance training and adequate protein. Always discuss major changes with a healthcare professional.

Why is my real-world progress slower than the calculator estimate?

Scale weight reflects water and glycogen as well as fat, and your body may adapt by reducing energy expenditure over time. Logging accuracy, activity levels, sleep, and stress also matter. Use this tool as a planning aid, not a guarantee.

Can this replace advice from a doctor or dietitian?

No. This calculator is for general information only. For personalized guidance—especially if you have medical conditions, take medications, or have a history of disordered eating—work with a qualified healthcare provider or registered dietitian.

fitness calculator

Calorie Deficit Time Calculator

Estimate time to reach a weight-loss goal using a daily calorie deficit.

Results

Estimated days: 70.00
Estimated weeks: 10.00

How to use this calculator

Decide on a realistic weight-loss goal in pounds. Many guidelines suggest aiming for gradual, sustainable loss rather than aggressive crash diets.
Estimate your daily calorie deficit. This is how many calories below maintenance you plan to eat on average (for example, 300–600 calories per day).
Enter your goal in pounds and your planned daily calorie deficit into the calculator.
Review the estimated days and weeks to reach that goal based on the 3,500-calorie-per-pound rule.
Experiment with different deficit sizes and goals to see how they change the timeline, keeping in mind what feels sustainable and healthy for you.

Inputs explained

Weight loss goal (lb): The total amount of weight you would like to lose, in pounds. For example, 5, 10, or 20 lb. Smaller, incremental goals are often easier to manage and track than very large numbers all at once.
Daily calorie deficit: How many calories below your estimated maintenance level you plan to eat each day on average. A 500-calorie-per-day deficit is a common example used in many articles, but the right number for you depends on your body, activity, and guidance from a professional.

How it works

The calculator uses the common heuristic that, on average, about 3,500 calories correspond to roughly one pound of body weight change.

First, we multiply your weight-loss goal in pounds by 3,500 to estimate the total calorie deficit required for that amount of weight loss.

Next, we divide that total required calories by your daily calorie deficit to estimate how many days it would take if your deficit stayed consistent.

Finally, we divide the days by 7 to convert to weeks, giving you both an approximate day count and week count.

In real life, progress is not perfectly linear—metabolic adaptations, water shifts, and adherence all influence actual results—so treat these numbers as planning estimates rather than promises.

Formula

We use a simple two-step model:\n\n1. Total calories to lose = Weight loss goal (lb) × 3,500 kcal/lb.\n2. Estimated days = Total calories to lose ÷ Daily calorie deficit.\n3. Estimated weeks = Estimated days ÷ 7.

When to use it

Estimating how long a given calorie deficit might take to move from your current weight toward a specific goal weight.
Comparing different deficits—for example, 300 vs. 500 vs. 700 calories per day—to see how much they change the projected timeline.
Planning phases of a weight-loss journey (for example, breaking a larger goal into multiple smaller goals with built-in maintenance breaks).
Setting expectations before starting a new nutrition plan so you are less likely to be discouraged by normal week-to-week fluctuations.

Tips & cautions

Bigger deficits are not always better. Very large calorie cuts can be hard to sustain, may increase hunger and fatigue, and can put lean mass at risk—talk with a healthcare or nutrition professional about what is appropriate for you.
Weight on the scale fluctuates daily due to water, glycogen, and digestion. Even with a consistent deficit, you may see plateaus or sudden drops; look at trends over several weeks, not single days.
Consider pairing this tool with a total daily energy expenditure (TDEE) calculator and a macros calculator so you can estimate maintenance, set a deficit, and allocate calories to protein, carbs, and fats.
Adjust the plan over time. As you lose weight or change your activity level, your maintenance calories can shift, so revisit your estimated deficit periodically.
The 3,500-calories-per-pound rule is a simplification. Actual fat loss depends on many factors including starting body composition, hormonal environment, and metabolic adaptation.
The calculator assumes a constant daily deficit and does not account for days where you eat at or above maintenance, diet breaks, or non-linear progress.
It does not differentiate between fat, water, and lean mass changes—the scale reflects all three.
This tool is for general educational purposes only and is not a substitute for individualized medical or nutrition advice.

Worked examples

Example 1: 10 lb goal with a 500-calorie deficit

Total calories to lose = 10 × 3,500 = 35,000 kcal.
Estimated days = 35,000 ÷ 500 = 70 days.
Estimated weeks = 70 ÷ 7 = 10 weeks. In practice, progress may be somewhat slower or faster depending on your body and adherence.

Example 2: 5 lb goal with a 300-calorie deficit

Total calories to lose = 5 × 3,500 = 17,500 kcal.
Estimated days = 17,500 ÷ 300 ≈ 58.3 days.
Estimated weeks ≈ 58.3 ÷ 7 ≈ 8.3 weeks—around two months of consistent effort for a modest, sustainable deficit.

Example 3: Comparing moderate vs aggressive deficits

You keep the same 15 lb goal but compare a 400-calorie deficit to a 700-calorie deficit.
At 400 kcal/day: total calories = 15 × 3,500 = 52,500; days ≈ 52,500 ÷ 400 ≈ 131.3; weeks ≈ 18.8.
At 700 kcal/day: days ≈ 52,500 ÷ 700 ≈ 75; weeks ≈ 10.7. The more aggressive plan is faster on paper, but may be harder to maintain comfortably.

Deep dive

Use this calorie deficit time calculator to estimate how many days and weeks it might take to reach a weight-loss goal based on the classic 3,500-calories-per-pound rule of thumb.

Enter your weight-loss goal in pounds and your planned daily calorie deficit to get a rough timeline, then experiment with different scenarios to see how changing the deficit affects your estimated finish date.

Ideal for people planning a new nutrition phase who want a simple, understandable way to translate daily calorie cuts into a big-picture weight-loss timeline—while remembering that real bodies do not follow perfect math.

FAQs

Is the 3,500-calories-per-pound rule accurate?: It is a widely used approximation, not a law of physics. It can provide a reasonable order-of-magnitude estimate for some people, especially in the early stages of weight loss, but individual responses vary and metabolism adapts over time.
Should I use a very large calorie deficit to lose weight faster?: Bigger deficits come with trade-offs: increased hunger, lower energy, potential loss of lean mass, and higher risk of rebound if the plan is too aggressive. Many people do better with a moderate deficit they can maintain alongside resistance training and adequate protein. Always discuss major changes with a healthcare professional.
Why is my real-world progress slower than the calculator estimate?: Scale weight reflects water and glycogen as well as fat, and your body may adapt by reducing energy expenditure over time. Logging accuracy, activity levels, sleep, and stress also matter. Use this tool as a planning aid, not a guarantee.
Can this replace advice from a doctor or dietitian?: No. This calculator is for general information only. For personalized guidance—especially if you have medical conditions, take medications, or have a history of disordered eating—work with a qualified healthcare provider or registered dietitian.

Related calculators

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TDEE Calculator

Estimate total daily energy expenditure (TDEE) based on BMR and activity level.

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Macro Calculator

Convert daily calories into protein, carb, and fat gram targets.

This calorie deficit time calculator uses simplified assumptions to estimate how long a daily calorie deficit might take to produce a given amount of weight loss. It does not account for individual health conditions, metabolic adaptations, medications, or other important factors and is not medical or nutrition advice. Always consult a qualified healthcare professional before making significant changes to your diet, exercise routine, or weight-loss plan.