How this calculator works
The static 7700 kcal/kg rule converts a daily energy difference into signed weekly weight change for non-pregnant adults. Loss is negative and gain positive. Intake below the sheet floor of 1200 kcal/day for females or 1500 for males is raised to that floor and labelled. These floors do not establish individual safety. Hall's dynamic model shows why real change slows and this linear forecast becomes unreliable. The result is an estimate for information only and is not medical advice.
Formula
Rate (kg/week) = (intake used - TDEE) x 7 / 7700. Rate (lb/week) = rate / 0.45359237. Weeks = signed goal / signed rate.
Worked example
At TDEE 2500 and intake 2000 kcal/day, signed change is -0.45 kg/week. A -10 kg goal takes about 22 weeks under the static assumption.
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Frequently asked questions
Why is a loss rate negative?
The equation reports signed mass change. A negative goal and negative rate produce a positive time.
What happens at maintenance?
A nonzero goal cannot be reached at a zero rate, so the tool returns a field error. A zero goal takes zero weeks.
Does the weekly rate stay the same over time?
No. The 7700 kcal/kg rule is static, so the forecast does not slow as the body adapts. Real change often does, which makes later weeks less reliable.