What this tool does
Enter calories and the percent of those calories you want from fat. The output is grams and the fat calorie slice. It will not design a Mediterranean pattern or a ketogenic one by itself — keto has its own tool with a carb cap.
How it works
Fat grams = calories × percent / 9. Dietary Guidelines for Americans commonly discuss about 20–35% of calories from fat for the general adult pattern. Below that for a long time is a preference that needs a reason. Above that can still work if protein is intact and calories match the goal.
Formula and methodology
Fat g = (kcal × fat%) / 9. The 9 kcal/g Atwater factor is an average. Actual metabolizable energy varies slightly by food. This is a planning identity, not a fatty-acid panel.
How to interpret the result
If protein is already set in grams, fat and carbohydrate share the remainder. Dropping fat to 10% to “be good” often makes meals miserable and can squeeze fat-soluble vitamins unless the rest of the diet is carefully built. Olive oil, nuts, dairy, and fatty fish are foods, not moral events.
Example
At 2,000 kcal and 30% fat: 67 g fat (600 kcal). At 2,000 kcal and 20%: 44 g. At 2,800 kcal and 30%: 93 g. The 67 g version is a typical mixed diet; the 44 g version is still workable if cooking oil is measured.
Common mistakes
- Confusing “low fat foods” with a low fat budget — many are high sugar.
- Ignoring oils poured in a pan and then logging a dry chicken breast.
- Setting 10% fat on a 1,600 kcal cut for months because the slider allowed it.
- Using this instead of the keto calculator when you actually want a carb cap.
When this estimate may be off
- You have been prescribed a fat-restricted medical diet (e.g., certain pancreatic or gallbladder contexts) this page does not encode.
- A large share of calories is MCT oil or alcohol, which the 9 kcal/g story oversimplifies.
- The calorie target is fictional.
- You need EPA/DHA targets; this tool only totals fat grams.