Calorie deficit calculator

How the calculator works

It starts with your maintenance calories, estimated with the Mifflin-St Jeor equation and an activity factor, exactly as in the TDEE calculator. Then it works out the deficit for your pace and projects your weight one week at a time:

• Maintenance = (10 × weight in kg + 6.25 × height in cm − 5 × age + 5 for men or − 161 for women) × activity factor.
• Daily deficit = pounds a week × 3,500 ÷ 7 (or kg a week × 7,700 ÷ 7), so 1 lb a week is about 500 calories a day.
• Each week, weight changes by (maintenance − calories eaten) × 7 ÷ 7,700 kg, and maintenance is worked out again from the new weight.
• Every 10 lb (5 kg) the plan recalculates your target from your new maintenance, so the pace holds.

Why the plan lowers your calories in steps

There are two honest ways to plan weight loss. You can keep eating the same amount, in which case your deficit shrinks as your body gets smaller and loss slows toward a plateau. Or you can keep the pace by eating a little less as you go. This calculator does the second, in steps you can actually follow: one calorie target until you’ve lost 10 lb, then a slightly lower one. Between steps the intake stays fixed, so the projection eases off slightly, just as real loss does. The plan never drops below 1,200 calories a day for women or 1,500 for men, the low end of the ranges in the 2013 AHA/ACC/TOS guideline for managing overweight and obesity; where that floor applies, it keeps the floor and lets the pace slow instead. It also caps the pace at 1% of your body weight a week.

Worked examples

• Lightly active woman, 20 lb to lose: 35 years old, 5 ft 7 in and 180 lb, aiming for 160 lb at 1 lb a week. Her maintenance is about 2,120 calories, so she starts at 1,630 a day. After the first 10 lb the plan lowers that to 1,570, and she reaches 160 lb in about 22 weeks. At her goal, maintenance is about 2,000. Staying at 1,630 the whole way would take about 23 weeks.
• Desk-bound man, 40 lb to lose: 45 years old, 5 ft 10 in and 230 lb, aiming for 190 lb at 1.5 lb a week. His maintenance is about 2,320 calories, so he starts at 1,580 a day. By his last 10 lb step, keeping the pace would mean eating under 1,500, so the plan holds at 1,500 and the pace eases. He reaches his goal in about 29 weeks, and his maintenance there is about 2,100.

How the pace changes the date

The same woman’s 20 lb goal at each pace. A faster pace means a bigger daily deficit and an earlier date, until the 1% cap applies.

At 2 lb a week she would need a deficit of about 1,000 calories, but 2 lb is more than 1% of her 180 lb, so the calculator uses 1.8 lb a week and tells you why.

What the estimate can’t tell you

This is a simplified model. Research by Kevin Hall and colleagues at the NIH showed that the body’s response to eating less is slow, taking roughly a year to reach half of the eventual change, and that the 3,500-calorie rule overstates long-term loss. Their model tracks fat and lean tissue, water and the way metabolism adapts, and it powers the NIH’s Body Weight Planner. Our projection includes one part of that, a smaller body burning less, but not the rest. Hall’s rule of thumb is that each 10 calories a day you eat less eventually lowers your weight by about a pound; the equations here account for only 5 to 9 calories of that, depending on activity. So for a long or large plan, expect real progress to be somewhat slower than shown, and use the NIH planner for a more detailed projection. Either way, your own scale over several weeks is the best guide: if the trend is slower or faster than the plan, adjust your calories a little and keep watching.

The calculator plans loss only. If your goal weight is under a BMI of 18.5 for your height, the bottom of the healthy range (see the BMI calculator), it stops the plan there. To gain weight or maintain, use the goal table in the TDEE calculator. To split your calories into protein, carbs and fat, try the macro calculator; the protein calculator shows how much protein you need each day.

Sources

• Hall KD, Sacks G et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet, 2011.
• National Institute of Diabetes and Digestive and Kidney Diseases. Body Weight Planner. NIH.
• Jensen MD, Ryan DH et al. 2013 AHA/ACC/TOS guideline for the management of overweight and obesity in adults. Circulation, 2014.
• Mifflin MD, St Jeor ST et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990.
• Centers for Disease Control and Prevention. Steps for losing weight. CDC.

This calculator gives an estimate for healthy adults. It isn’t medical advice. If you have a health condition, take medication that affects your weight or appetite, are pregnant or breastfeeding, or have a history of disordered eating, talk to your doctor or a registered dietitian before starting a diet.