TDEE Confidence Range Calculator

First, the tool computes a baseline TDEE using your selected maintenance method (e.g., Mifflin-St Jeor) and activity multiplier (e.g., moderate, light, very active). Next, it converts your recent weight trend (lb/week or kg/week) into a daily calorie adjustment using practical approximations (about 500 kcal/day per 1 lb/week; 1100 kcal/day per 1 kg/week). Finally, it outputs a confidence range (lower bound, midpoint, upper bound) that tightens with longer, steadier trends and widens when the trend is short or near zero.

Scale weight reflects more than fat change (water, sodium, glycogen, digestion, and normal day-to-day variability), so short windows can mislead the calibration. The calculator simplifies these effects by widening the confidence interval when your trend window is brief or the weight trend is close to zero. Also, higher activity levels typically introduce more day-to-day noise, so confidence may be lower even when the trend looks plausible.

If your weight trend is extremely large, the tool warns that the assumption “weight change ≈ energy balance” may be violated by non-fat factors. If the trend window is under 3 weeks (or your trend is very close to zero), it labels the result low confidence and leans more on the formula estimate. If the trend-calibrated estimate differs from your formula estimate by more than ~10%, the tool flags that you likely need calibration (i.e., more data and/or reassessing your inputs).

If you choose “custom calorie estimate,” your custom baseline anchors the formula side before the trend adjustment—so you should keep activity settings consistent. If trend window is valid but trend is near 0, expect a wider confidence range and a recommendation to rely more on the formula estimate. If units don’t match (lb with lb/week, kg with kg/week), the tool enforces consistency to avoid nonsensical calorie adjustments.