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IF Results Estimator

An honest range rather than a promise. It assumes a weekly calorie deficit per protocol — 1,500 on 14:10 up to 4,200 on one meal a day — scales it for consistency, diet quality and experience, converts at 7,700 calories per kilogram, and caps the result at 1.5 percent of body weight a week. Every assumption is listed below.

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How this is calculated

This estimator multiplies four assumptions together, and it is only worth reading if you know what all four are.

It starts from an assumed weekly calorie deficit for each protocol: 1,500 for 14:10, 2,100 for 16:8, 2,800 for 18:6, 3,500 for 20:4 and 4,200 for one meal a day. Those figures are this site's own assumptions about how much less people tend to eat as the window narrows. They are not measured effects of fasting, and nobody has published a table like this.

That weekly deficit is then scaled three times: by how consistent you say you will be (0.5, 0.8 or 1.0), by how much attention you will pay to what you eat (0.7, 1.0 or 1.2), and by where you are starting from (1.15 for a beginner, 1.05 returning, 1.0 with some experience). The three scenarios apply a final 0.6, 1.0 or 1.3. Calories become kilograms at roughly 7,700 per kilogram, and the result is capped at 1.5 percent of body weight a week, because faster than that is mostly not fat.

Three quarters of the loss is counted as fat and the rest as lean tissue and water, which is where the body-fat change comes from. Every number is then shown as a range of plus or minus 15 percent, and the honest reading of that range is still "a plan, drawn from assumptions" rather than a forecast. Anything that promises you a precise number 90 days out is guessing; this page at least shows its guesses.

Where this comes from

  1. 1. Body Weight Planner — National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health
  2. 2. Effects of Intermittent Fasting on Health, Aging, and Disease — de Cabo & Mattson, New England Journal of Medicine, 2019 (PubMed)

Nothing on this site is medically reviewed — it cites its sources so you can check them. Read our editorial policy. Method last checked 21 August 2026.

Setting realistic expectations before starting intermittent fasting helps you stay committed when progress feels slow. Knowing what typical 30, 60, and 90-day results look like gives you benchmarks to measure against and reassurance that you are on the right track.

This estimator accounts for the factors that matter most: your starting point, chosen protocol, and consistency level. It provides a grounded projection rather than the exaggerated promises you find elsewhere, because sustainable results come from sustainable habits.

Frequently Asked Questions

How much weight can I lose in 30 days with intermittent fasting?
Most people lose 4-8 pounds in their first 30 days of intermittent fasting, though this varies widely based on starting weight, protocol, consistency, and overall diet quality. Some of the initial loss is water weight, with more consistent fat loss following in months two and three.

Does consistency matter more than the fasting protocol?
Absolutely. Research consistently shows that adherence is the strongest predictor of results. Someone who follows 16:8 seven days a week will typically see better results than someone who attempts OMAD but only manages it three days a week. Choose the protocol you can stick with.

How accurate are these intermittent fasting estimates?
These projections are based on published research and population averages, but individual results vary significantly. Factors like metabolic health, hormonal status, sleep quality, stress levels, and diet composition all influence outcomes. Use the estimates as a general guide, not a guarantee.

What is the biggest factor in intermittent fasting success?
Consistency over time is the single biggest factor. Beyond that, the quality of food during your eating window, adequate protein intake, regular physical activity, sufficient sleep, and proper hydration all play significant roles in determining your results.

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