Fasted FASTED

Weight Loss Calculator

A kilogram of body tissue is roughly 7,700 calories, so a 550-calorie daily deficit is about half a kilogram a week and 1,100 is about a kilogram. Give it your start weight, goal weight and deficit, and it prints the weekly rate, the milestone dates and the week you arrive — with or without a fasting allowance on top.

centimeters
kilograms
kilograms
100 kcal 1200 kcal

How this is calculated

Maintenance calories come from Mifflin-St Jeor — 10 × weight in kilograms + 6.25 × height in centimetres − 5 × age, + 5 for men or − 161 for women — multiplied by an activity factor between 1.2 and 1.9. Your deficit is then either the one you set or the one your goal date demands, and weekly loss is that deficit × 7 ÷ 7,700, because roughly 7,700 calories is the energy in a kilogram of body tissue.

Two things about that division are worth knowing. It is linear and reality is not: a smaller body burns fewer calories, so the same deficit buys less loss every month and the far end of a long projection is optimistic. And it says nothing about what the lost weight is made of — the first fortnight of any deficit is largely water and glycogen, which is why the scale drops fast and then appears to stop.

The intermittent-fasting selector adds a flat allowance to the daily deficit: 300 calories for 16:8, 400 for 18:6, 500 for longer fasts. That allowance is this site's own assumption about how much less people tend to eat when the window closes, not a measured effect of fasting itself — the trials that compare time-restricted eating against plain calorie counting at matched intake mostly find the difference small. If you would rather not lean on it, set the approach to none and the calculator works on the deficit alone.

The milestone dates and the projection chart are drawn from the same straight line, and daily intake is clamped so it never falls below 1,200 calories.

Where this comes from

  1. 1. A new predictive equation for resting energy expenditure in healthy individuals — Mifflin et al., American Journal of Clinical Nutrition, 1990 (PubMed)
  2. 2. Body Weight Planner — National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health

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.

Having a realistic timeline for your weight loss goal keeps you motivated and prevents the discouragement that comes from unrealistic expectations. Understanding how long the journey will take helps you commit to sustainable habits rather than crash diets.

Intermittent fasting is particularly powerful for long-term weight loss because it is a lifestyle pattern rather than a temporary diet. This calculator shows you how consistent fasting and a moderate deficit add up over weeks and months to meaningful, lasting change.

Frequently Asked Questions

Is losing 1-2 pounds per week realistic?
Yes, 1-2 pounds per week is widely considered the gold standard for sustainable weight loss. This requires a daily deficit of 500-1,000 calories. Most health professionals recommend staying at the lower end (1 pound per week) to preserve muscle mass and avoid metabolic slowdown.

Does intermittent fasting speed up weight loss?
IF can accelerate fat loss by improving insulin sensitivity, increasing growth hormone levels, and promoting fat oxidation. However, the primary benefit is that it naturally helps people maintain a calorie deficit. Studies show similar weight loss results to calorie restriction, but IF practitioners often find it easier to sustain.

What should I do about weight loss plateaus?
Plateaus are normal and happen to everyone. Your body adapts to lower calorie intake by reducing energy expenditure. Solutions include recalculating your TDEE at your new weight, adding resistance training, adjusting your fasting window, or taking a planned diet break for 1-2 weeks.

How accurate are weight loss projections?
Projections are useful as a general guide but cannot account for individual metabolic variation, water retention, hormonal fluctuations, and adaptation. Expect the timeline to be approximate. The first few weeks often show faster loss due to water weight, followed by a steadier pace.

Go deeper

weight loss · 8 min read

How Much Weight Can You Lose with Intermittent Fasting?

Realistic intermittent fasting weight loss expectations by week, month, and year. Science-backed numbers so you know exactly what results to expect.

weight loss · 7 min read

Intermittent Fasting Results After 3 Months: A Realistic Timeline

What does 3 months of intermittent fasting actually produce? Real timelines, realistic numbers, and what to expect month by month over 90 days.

weight loss · 8 min read

Intermittent Fasting for Weight Loss: Does It Actually Work?

Does intermittent fasting actually work for weight loss? We break down the science, real results, and practical tips to help you decide if IF is right for you.

More Free Tools

Calorie Deficit Calculator

Calculate the right calorie deficit for your weight loss goal. See daily calories, weekly deficit, and time to reach your target weight.

TDEE Calculator

Calculate your Total Daily Energy Expenditure based on age, weight, height, and activity level. Free, instant, no signup.

IF Results Estimator

Estimate your intermittent fasting results based on protocol, consistency, and starting stats. See 30, 60, and 90-day projections.

Track your fasting consistency in the Fasted app

The Fasted app tracks every fast and builds your consistency streak, which is the single most important factor in reaching your goal weight.

Download on the App Store Get it on Google Play

Free to use — no account required