The NIH Body Weight Planner is a free tool from the National Institute of Diabetes and Digestive and Kidney Diseases. You enter your details and a goal, and it estimates how many calories you need to maintain your weight, reach your goal by a date and stay there afterwards. Treat the numbers as a starting point, then adjust based on what the scale and tape measure do.
For a simpler, less nerdy method, read how to calculate a calorie deficit without obsessing.
What does the NIH Body Weight Planner do?
According to the NIDDK, the planner helps you "reach a goal weight within a specific time period and to maintain it afterwards." It gives you three calorie targets: what you need to maintain your current weight, what you need to reach your goal weight, and what you need to hold that new weight.
It is built on a model published in The Lancet in 2011. You can read about the research behind the Body Weight Planner on the NIDDK site.
What do you need to enter?
- Your starting weight, sex, age and height.
- Your physical activity level, on a scale from 1.4 (sedentary) to 2.5 (very active).
- Your goal weight and the date you want to reach it.
- Optionally, planned changes in activity.
Be honest about your activity level. Most men overestimate it. If you sit all day and train three times a week, you are probably nearer the lower end than you think.
How do you use the results?
Use the first number as your baseline and the second as your target, then check it against reality for a few weeks:
- Enter your details honestly.
- Pick a realistic timeline. The CDC says about 1 to 2 pounds a week is more likely to be kept off.
- Eat to the target for two to three weeks.
- Check your weekly average weight and waist.
- Adjust by a small amount if nothing moves.
It is a model, not a prophet. Your real life will wiggle around it.
What are the limits?
The NIH itself lists several cautions:
- It notes that people often underestimate how much they eat.
- Results can be too high if you have an abnormally low metabolism or are very sedentary.
- The minimum daily intake it allows is 1,000 calories.
- It is designed for adults 18 and over, and not for pregnant or breastfeeding women.
- A health care provider who knows your history is the best person to advise you.
A very short timeline will push the target calories down uncomfortably far. If the plan feels like starvation, lengthen the timeline.
Should you eat back exercise calories?
The planner lets you add planned activity changes, so it already includes them. Don't add them again from your watch. Watches and gym machines tend to be generous.
Is it better than a simple calculator?
It is more detailed, because it accounts for the fact that you need fewer calories as you get lighter. That makes it handy for bigger goals. For small goals, a simple weekly check works just as well. Either way, track your weekly average weight, your waist and your lifts, not just one morning's number.
What about protein?
The planner only handles calories. Aim for 1.2 to 1.6 grams of protein per kilogram of body weight, the range in the Dietary Guidelines for Americans 2025 to 2030, and keep lifting so you keep muscle. See how much protein you need to lose fat.
The bottom line
Use the NIH Body Weight Planner to get a sensible starting number, choose a realistic timeline and adjust from real results. Then start the 4-week restart plan so the training matches the food.
Go train, FATBOY.
This article is general information, not medical advice. If you have a health condition or take regular medication, talk to your doctor or a dietitian before changing your diet.
- calories
- nutrition