Deficitly
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How many calories do you burn a day doing nothing?
Lying still all day, a 40-year-old woman of 70 kg (154 lb) and 165 cm (5′5″) burns about 1,370 calories, and a 40-year-old man of 85 kg (187 lb) and 178 cm (5′10″) about 1,770. This is your basal metabolic rate (BMR). On a lazy day at home you burn more: roughly 1,670 and 2,160.
Resting burn for women
| Weight | Age 25 | Age 40 | Age 55 | Age 70 |
|---|---|---|---|---|
| 50 kg 110 lb | 1,250 | 1,170 | 1,100 | 1,020 |
| 60 kg 132 lb | 1,350 | 1,270 | 1,200 | 1,120 |
| 70 kg 154 lb | 1,450 | 1,370 | 1,300 | 1,220 |
| 80 kg 176 lb | 1,550 | 1,470 | 1,400 | 1,320 |
| 90 kg 198 lb | 1,650 | 1,570 | 1,500 | 1,420 |
| 100 kg 220 lb | 1,750 | 1,670 | 1,600 | 1,520 |
| 110 kg 243 lb | 1,850 | 1,770 | 1,700 | 1,620 |
Resting burn for men
| Weight | Age 25 | Age 40 | Age 55 | Age 70 |
|---|---|---|---|---|
| 60 kg 132 lb | 1,590 | 1,520 | 1,440 | 1,370 |
| 70 kg 154 lb | 1,690 | 1,620 | 1,540 | 1,470 |
| 80 kg 176 lb | 1,790 | 1,720 | 1,640 | 1,570 |
| 90 kg 198 lb | 1,890 | 1,820 | 1,740 | 1,670 |
| 100 kg 220 lb | 1,990 | 1,920 | 1,840 | 1,770 |
| 110 kg 243 lb | 2,090 | 2,020 | 1,940 | 1,870 |
| 120 kg 265 lb | 2,190 | 2,120 | 2,040 | 1,970 |
BMR is not what you burn on a lazy day
Even on the couch you stand up, make food and fidget, and digesting what you eat costs about 10% of the calories in it. Deficitly adds 10% of your BMR for basic daily life and the cost of digestion, then your steps and workouts on top. The full picture is in how many calories you need to maintain your weight.
Why it drops with age
The equation takes off about 5 calories a day per year of age, mostly because people tend to lose muscle as they get older. Staying active and lifting weights slows that down.
"Never eat below your BMR"?
A popular rule, but not a precise one. Your real burn is well above your BMR, so eating at your BMR is already a sizeable deficit for most people. Deficitly uses fixed minimums instead: 1,200 calories a day for women and 1,500 for men. More on that in is 1,200 calories a day safe?