by Don Heatrick

B-class and A-class fighters weigh-in the day before the fight. Having 24-hours to rehydrate and restore muscle glycogen allows significant, safe, temporary weight reduction. However, when starting out on novice or C-class shows, you’ll be expected to weigh-in and fight on the same day. This drastically changes things.

Starting Point – Body Composition

Don same day weigh in sasiprapa gym

First things first. Your body composition needs to be right before you consider any kind of “weight cut” for a fight. In my opinion, the weight cut is the temporary distortion of your bodyweight through safe manipulation of body fluid levels in the final week of the fight preparation. It’s not the loss of unnecessary body fat, this should already be on point.

Body fat levels should be between 6-13% for male fighters and 14-20% for female fighters. If needed, trim your fat levels in preceding weeks – and this weight loss must be from fat alone, not muscle. Muscle is hard earned and is not only responsible for your strength, power and stamina, but also stabilises your body, protects from injury and burns up your calories. Lose muscle and you’re performance will suffer, your body is less robust, can breakdown, and you’ll get fat much easier.

How Much to Cut

Most novice shows only allow about 3-4 hours between the weigh-in and the first fight. Your coach should have an itinerary from the promoter and can advise you how long you’re likely to have between the weigh-in and your fight as a minimum, but always ‘err’ on the side of caution. Novice shows are the most likely to suddenly change fight order and timings etc. My advice, expect to have 4-hours max.

With such a limited amount of time to rehydrate and replenish energy stores, your weight cut needs to be sensible to allow you to fight your best. Fighting at your lightest doesn’t necessarily mean fighting at your best – something I’ve personally experienced and learned the hard way. Temporary weight loss for a same day weigh-in should come almost entirely from mild dehydration. You must fully rehydrate before getting in the ring. If you fight while even mildly dehydrated, your performance falls by a minimum of 10%. Being naturally a bit bigger than the other guy, but feeling weak and fatigued, squanders any advantage and is frustrating as hell.

The Effect of Dehydration on Performance

The Effect of Dehydration on Performance

My recommendation is to cut no more than 2-3% of your body weight through dehydration when weighing-in on the same day as the fight. At this level of dehydration, with the correct rehydration strategy you can realistically be back to full weight (and optimum hydration) within 4-hours – before you climb though the ropes.

Experiment with dehydrating by 2-3% of your bodyweight and practice rehydrating again before a training session to see how you feel. Find out what you can personally tolerate now, not on the day of the fight.

What’s My (Same-Day) Fight Weight?

Same Day Fight Weight Table

Same Day Fight Weight Table

If your body fat percentage is too high, you must estimate how much body fat you can realistically lose between now and the fight date. I’d recommend you plan for a maximum rate of 0.5kg of fat loss per week. If you half the number of weeks you have until your fight, that’s the amount of weight loss (in kg) you can lose in fat alone in that time. You then need to take this estimated (fully hydrated) weight and then factor in 2 or 3% of mild dehydration (depending on how much you can tolerate – remember, test this in training). Take your estimated final hydrated weight and multiply by 0.98 if you intend to dehydrate by 2% bodyweight, or 0.97 if 3% dehydration is okay for you.

Take a look at the ‘Same Day Fight Weight Table’ for a quick idea of your fight weight.


Extra caution must be taken with junior fighters. Firstly they’re growing! Don’t force them to fight at unrealistic weights. They’re body fat levels should be within the healthy ranges I’ve stated above, and they should never cut muscle weight (neither should adults). Maturing bodies need extra nutrients to develop healthy joints, bones, muscle and organs etc. The dehydration levels I’ve recommended are safe for juniors too, but realise that these levels are a percentage of the fighters body weight. The lighter the fighter, the less weight this will amount to.

As with adults, the primary concern is the health and performance of the fighters. Don’t get caught up in the silly ‘lighter is more competitive’ attitude. A robust, well muscled, coordinated body will serve you best not only during the fight, but also during the weeks of training leading up to the fight. If you want a successful fight career, start with the right attitude, or risk it prematurely finishing.

What Next?

In this first part of my article, I’ve outlined my thoughts on how much weight you can cut for a same day weigh-in and why… in part 2 I discuss my recommendations for how you cut weight.

Please let me know your thoughts or questions in the comments below.

Don Heatrick

Founder of Heatrick Strength and Conditioning

Don Heatrick is a family man from the UK, former mechanical design engineer, European Muay Thai silver medallist, former pro Thai boxer (ranked 4th in UK while aged 40-years), a Muay Thai coach, podcast host, and the go-to expert on Muay Thai performance training with over 25 years of coaching experience.

Don helps ambitious fighters and coaches take their game to the next level by bridging the gap between Strength & Conditioning, Performance Science, and Muay Thai.

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