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Should you cut or bulk?
Cut first if your waist is half your height or more, or your body fat is high. If you are lean and want size, bulk. Otherwise your goal decides, and recomposition, eating near maintenance while you train hard, is a real option. The check below makes the call from your numbers and links to the right calculator.
Check whether to cut or bulk
Enter your body fat if you know it, or your waist. Weight alone cannot tell muscle from fat, and that is what the call turns on.
One more number
Enter your body fat or your waist. Weight alone cannot tell muscle from fat, and that is what this call turns on. To measure your waist, see how below.
For adults 19 and over. Not for pregnancy or breastfeeding, or for anyone with a past or present eating disorder. General information, not medical advice.
When to cut, bulk or recomp
Cut first if your waist is half your height or more, or your BMI is 35 or more: NICE links both to raised health risk (NICE, 2025). Cut first too if your body fat is 20% or more (men) or 30% or more (women). Bulk if you are under 15% or 25% and want size. Between those lines, your goal decides. Under a BMI of 18.5, where NICE’s healthy range starts, the check never suggests a cut.
| Call | When | Why |
|---|---|---|
| Cut first | Waist at least half your height, or a BMI of 35 or more | NICE links both to raised health risk, and uses the waist check only under a BMI of 35 (NICE, 2025) |
| Lean bulk or recomp | A BMI under 18.5. A recomp if you want to look leaner, or your waist or body fat is high | NICE’s healthy range starts at 18.5, so the check never suggests a cut below it (NICE, 2025) |
| Cut first | Body fat 20% or more (men) or 30% or more (women) | The leaner you start a bulk, the more of the gain is lean mass (Chow and Hall, 2008) |
| Recomp | New to lifting, body fat over that line, waist under half your height | Newer lifters can build muscle while losing fat (Barakat et al., 2020) |
| Lean bulk | Body fat under 15% (men) or 25% (women), and you want size | Lean lifters put more of a gain into lean mass; a slow cut is the other option |
| Your goal decides | Anything in between | Leaner: a cut. Bigger: a lean bulk. Both: a recomp. |
The body fat lines are a rule of thumb: no trial sets them. They rest on Forbes’s model, below, and on advice that leaner lifters should cut more slowly (Ruiz-Castellano et al., 2021). If you have no body fat reading, the waist does the job: it is the check NICE uses, and it allows for muscle.
How to measure your waist
Find the bottom of your ribs and the top of your hips, wrap a tape measure around your waist midway between them, which is just above the belly button, and breathe out naturally before you read it (NICE, 2025). Divide by your height in the same units: a 38 in waist at 5 ft 7 in (67 in) gives 38 ÷ 67 = 0.57.
A ratio of 0.4 to 0.49 is healthy, 0.5 to 0.59 means increased health risk, and 0.6 or more high. NICE says the ratio works for men and women of all ethnicities with a BMI under 35, adults with high muscle mass included, and advises keeping your waist under half your height (NICE, 2025).
| Height | Waist at 0.5 | Waist at 0.6 |
|---|---|---|
| 5 ft 2 in (157 cm) | 31 in (79 cm) | 37.2 in (94 cm) |
| 5 ft 4 in (163 cm) | 32 in (81 cm) | 38.4 in (98 cm) |
| 5 ft 6 in (168 cm) | 33 in (84 cm) | 39.6 in (101 cm) |
| 5 ft 8 in (173 cm) | 34 in (86 cm) | 40.8 in (104 cm) |
| 5 ft 10 in (178 cm) | 35 in (89 cm) | 42 in (107 cm) |
| 6 ft 0 in (183 cm) | 36 in (91 cm) | 43.2 in (110 cm) |
| 6 ft 2 in (188 cm) | 37 in (94 cm) | 44.4 in (113 cm) |
Why start a bulk lean?
Because the leaner you are, the more of each kilo you gain is lean mass rather than fat. By Forbes’s model, at 80 kg about 57% of a small gain is lean mass at 10% body fat, 39% at 20% and 30% at 30% (Chow and Hall, 2008).
| Body fat | Fat | Lean share |
|---|---|---|
| 10% | 8 kg (18 lb) | 57% |
| 15% | 12 kg (26 lb) | 46% |
| 20% | 16 kg (35 lb) | 39% |
| 25% | 20 kg (44 lb) | 34% |
| 30% | 24 kg (53 lb) | 30% |
| 35% | 28 kg (62 lb) | 27% |
Overfeeding studies point the same way: weight gained by thin people was 60 to 70% lean, against 30 to 40% in people with obesity (Forbes, 2000). Both come from people who were not lifting, so read the numbers as a guide to direction, not a forecast for a lifter. The model works in reverse on a cut, too: the leaner you are, the more of each kilo lost is lean mass, one reason leaner lifters should diet more slowly (Ruiz-Castellano et al., 2021).
Skinny fat: should you cut or bulk?
Usually neither: recomp. If your body fat is high but your waist is under half your height and you are new to lifting, eat around maintenance, keep protein at 1.6 to 2.2 g per kg of body weight a day (Morton et al., 2018) and train hard. Newer lifters can build muscle and lose fat at the same time (Barakat et al., 2020).
A steep cut works against that: in a meta-analysis, a deficit of about 500 kcal a day was enough to stop lifting adding lean mass (Murphy and Koehler, 2022). And protein matters most when you are not in a surplus: young men dieting hard on 2.4 g of protein per kg gained 1.2 kg of lean mass in 4 weeks, against 0.1 kg on 1.2 g (Longland et al., 2016).
Judge a recomp by your waist and your lifts, not the scale: if your waist holds or shrinks while your lifts climb, it is working. When you want to speed things up, the cutting calculator and the bulking calculator set the calories, and the maintenance calculator gives the starting point for a recomp.
Questions
Should I cut or bulk at 15% body fat?
For a man, 15% is where this check’s lean band ends: under 15%, bulk if you want size; from 15 up to 20%, your goal decides. For a woman, 15% is far under the 25% lean line, so bulk if you want size. No trial sets these lines; they are a rule of thumb that rests on Forbes’s model (Chow and Hall, 2008).
Should I cut or bulk at 20% body fat?
For a man, 20% is where this check says cut first, unless you are new to lifting and your waist is under half your height, when a recomp suits. By Forbes’s model, at 80 kg about 39% of a small gain is lean mass at 20% body fat, against 57% at 10% (Chow and Hall, 2008). For a woman, 20% is under the 25% lean line, so bulk if you want size.
Should beginners cut or bulk?
It turns on the waist. With a waist under half your height, a new lifter can recomp, eating around maintenance with protein high, because newer lifters can build muscle and lose fat at the same time (Barakat et al., 2020). With a waist at half your height or more, cut first (NICE, 2025). A lean beginner who wants size can bulk at up to 0.5% of body weight a week (Iraki et al., 2019).
What is a recomp?
Short for body recomposition: building muscle and losing fat at the same time, usually by eating around maintenance with high protein while training hard. It comes easiest to newer lifters, but a review found it in trained lifters too (Barakat et al., 2020). Progress shows in your waist and your lifts more than on the scale.
Is BMI useful for lifters?
Only as a rough first check. BMI cannot tell muscle from fat, and NICE advises reading it with caution in adults with high muscle mass. Waist-to-height works for them below a BMI of 35, so this check uses it: keep your waist under half your height (NICE, 2025).
How long should I cut before bulking?
Until your waist is under half your height and, if you track it, your body fat is under the line this check uses: 20% for men, 30% for women. At 0.7% a week, losing 5% of your weight takes about 7 weeks and 10% about 15, re-running the numbers as you go.
Sources
- Barakat C, Pearson J, Escalante G, Campbell B, De Souza EO (2020). Body recomposition: can trained individuals build muscle and lose fat at the same time?. Strength and Conditioning Journal 42(5):7-21. doi:10.1519/SSC.0000000000000584
- Chow CC, Hall KD (2008). The dynamics of human body weight change. PLoS Computational Biology 4(3):e1000045. doi:10.1371/journal.pcbi.1000045
- Forbes GB (2000). Body fat content influences the body composition response to nutrition and exercise. Annals of the New York Academy of Sciences 904:359-365. doi:10.1111/j.1749-6632.2000.tb06482.x
- Iraki J, Fitschen P, Espinar S, Helms E (2019). Nutrition recommendations for bodybuilders in the off-season: a narrative review. Sports 7(7):154. doi:10.3390/sports7070154
- Longland TM, Oikawa SY, Mitchell CJ, et al. (2016). Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial. American Journal of Clinical Nutrition 103(3):738-746. doi:10.3945/ajcn.115.119339
- Morton RW, Murphy KT, McKellar SR, et al. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine 52(6):376-384. doi:10.1136/bjsports-2017-097608
- Murphy C, Koehler K (2022). Energy deficiency impairs resistance training gains in lean mass but not strength: a meta-analysis and meta-regression. Scandinavian Journal of Medicine & Science in Sports 32(1):125-137. doi:10.1111/sms.14075
- National Institute for Health and Care Excellence (2025). Overweight and obesity management. NICE guideline NG246, last updated 8 January 2026. nice.org.uk/guidance/ng246
- Ruiz-Castellano C, Espinar S, Contreras C, et al. (2021). Achieving an optimal fat loss phase in resistance-trained athletes: a narrative review. Nutrients 13(9):3255. doi:10.3390/nu13093255
Each figure quoted from a study was checked against the paper, or its abstract where the full text could not be read. Found an error? Email founder@topsets.app and the page will be corrected and its date updated.