Three hard gym sessions plus a sedentary desk job the other four days averages out to lightly active, not moderately active — overestimating activity is the single most common reason a calorie estimate ends up wrong.
TDEE multipliers (1.2 to 1.9) are meant to represent your typical week, not your best day — picking one level too high can inflate a calorie estimate by 200-400 kcal a day, enough to stall a genuine deficit or surplus.
Estimate with the rule, then check it against the calculator that models it properly.
Open TDEE & Calorie Calculator →