Weight Change Simulator

Cutting and bulking both come down to calorie balance (intake − expenditure). Since 1 kg of body fat corresponds to roughly 7,200 kcal, a known daily balance lets you estimate your rate of change. This tool projects your weight over 1–24 weeks from your balance, and can also work backwards from a goal weight and deadline to the daily balance you need.

How to use this tool

First estimate your daily expenditure with the TDEE Calculator, then enter the difference between it and your actual intake (±kcal). Negative to cut (e.g. −300), positive to bulk. If you have a clear goal, use the "work back from goal" mode to see the required balance.

Safe rates of change

For fat loss, 0.5–1.0% of body weight per week is a sustainable pace that preserves muscle (0.35–0.7 kg/week at 70 kg). Faster cuts raise the risk of muscle loss, metabolic slowdown and rebound. For lean bulking, around 0.25–0.5% per week keeps fat gain in check. This tool warns when your pace exceeds 1% per week.

Why reality drifts from the projection

Daily weight swings with water, glycogen and food in transit, and TDEE itself falls as a cut progresses (metabolic adaptation), so real-world change is usually slower than projected. Review your weekly average every 2–4 weeks and adjust the balance. The PFC Calculator helps structure the diet itself.

What "7,200 kcal per kilogram" really means

The figure underpinning most diet maths — roughly 7,200 kcal of deficit per kilogram of body fat — is derived from the energy density of adipose tissue. Actual weight change also includes water, glycogen and lean tissue, so loss usually runs ahead of the calculation early on and behind it later. A drop of one or two kilograms in the first few days of a diet is common, and most of it is glycogen and the water bound to it.

Why plateaus happen

Losing weight lowers basal metabolism on its own. Add a reduced thermic effect of food and a drop in unconscious activity (NEAT), and the same intake no longer produces the same deficit. That combination is what a plateau after a few weeks actually is. The response is to recalculate intake or deliberately raise activity — cutting food further without doing either tends to deepen the metabolic adaptation.

A realistic rate of loss

To preserve muscle while losing fat, 0.5–1% of body weight per week is a workable target — about 0.35 to 0.7 kg a week at 70 kg. Faster than that and lean mass losses rise, along with the likelihood of regain. Plan for plateaus by revisiting intake every two to four weeks against measured weight trend rather than the original projection. For total expenditure, see the TDEE calculator.