Best Mass Gainer UK: Best Options Compared for 2026

Optimum Nutrition Serious Mass is the best overall UK mass gainer in 2026, delivering 1,250 calories and 50g of protein per serving with the widest UK retail availability of any mass gainer on this list. Applied Nutrition Critical Mass Professional is the highest-protein option at 42g of protein per 100g and carries Informed Sport certification. Warrior Mass Gainer is the price leader with the lowest cost per 100g.

A mass gainer is a high-calorie protein blend. The base is usually whey protein concentrate or a whey, casein, and egg blend. Most of the calories come from carbohydrates, whether that is maltodextrin in cheaper products or rolled oats and oat flour in better ones, with a smaller fraction from fats such as medium-chain triglycerides or flaxseed. Some mass gainers add creatine, vitamins, or digestive enzymes, though most of these extras are cheaper to buy separately.

The honest job of a mass gainer is to make it easier to hit a calorie surplus when food alone is not getting you there. Two scoops blended with milk delivers 600 to 1,250 kcal in 90 seconds. That convenience is what you are paying for, not the ingredients themselves.

Optimum Nutrition Serious Mass is the benchmark mass gainer on UK shelves, delivering 1,250 calories and 50g of protein per 334g serving, the largest serving size and one of the most balanced protein-to-carb ratios in the category. It comes in 2.7kg and 5.4kg bags from every major UK retailer including supermarkets, and Trustpilot taste scores sit around 4.3 out of 5 across UK reviewers.

Applied Nutrition Critical Mass Professional is the highest protein density mass gainer on this list at 42g protein per 100g, well above the 15 to 25g per 100g typical at the cheap end of the category. It comes in a 6kg bag, carries Informed Sport certification, and its lean-mass formula keeps the carb-to-protein ratio tighter than Serious Mass for anyone who wants calories without the maltodextrin spike.

Warrior Mass Gainer is the cheapest credible mass gainer on UK shelves at around £0.52 per 100g for the 5kg bag. Protein density is lower than the Applied or Optimum Nutrition picks, closer to 20g per 100g, but the calorie density is solid and the ingredient list is straightforward. If budget is the constraint and you just need calories in, this is where to start.

Mutant Mass uses some of the largest serving sizes in the UK market, with 322g per scoop delivering well over 1,000 calories. It suits genuine hard gainers who struggle to eat enough whole food, though the trade off is taste fatigue: a 6.8kg bag at 322g servings runs out in roughly 21 days, which is a lot of the same shake in a short window.

MyProtein's mainline mass gainer rarely competes on list price but becomes the cheapest UK mass gainer during Impact Week sales, typically 50 to 60% off. The best approach is to wait for the sale, buy in bulk, and store it dry. Outside of sale periods it sits mid pack on value.

The two metrics often pull in opposite directions. A 1,250-calorie mass gainer like Serious Mass leans heavier on carbs, combining maltodextrin and oats, and lighter on protein per 100g. A lean mass gainer like Applied Nutrition Critical Mass Professional pushes protein density up and total calorie density down.

The right pick depends on your bottleneck. If you struggle to eat enough food but already hit 1.6 to 2g of protein per kg, prioritise calorie density. If your diet is already calorie dense but protein poor, prioritise protein density instead. For most lifters in a normal bulk, the practical difference is smaller than the price gap suggests.

1. 1

   Under £25, 2 to 3kg bag: Warrior Mass Gainer or Mutant Mass 2.27kg. Lowest cost per 100g but lower serving counts.

2. 2

   £25 to £40, 5 to 6kg bag: Optimum Nutrition Serious Mass 5.4kg. The sweet spot for value plus brand reliability.

3. 3

   £40 to £60, 5 to 6kg bag: Applied Nutrition Critical Mass Professional. Highest protein density, Informed Sport certified.

4. 4

   £60 and above, 6.8kg bag: Mutant Mass 6.8kg. Largest serving sizes, lowest cost per 1,000 kcal in the volume tier.

A DIY mass gainer made from cheap whey concentrate, instant oats, and peanut butter consistently beats commercial mass gainers on cost per calorie. The DIY route saves around 40 to 60% per shake. The trade off is time and texture: blending oats takes longer than mixing maltodextrin and the result is grittier. If you have a blender and 90 seconds, DIY usually wins. If you need to mix with water in a shaker bottle at the gym, commercial wins.

To go DIY, start with the cheapest whey concentrate in the UK, then add 80 to 100g of oats and a tablespoon of peanut butter for a 500 to 700 kcal shake.

For a fuller breakdown see affordable mass gainer UK and cheapest mass gainer UK by ingredients.

1. 1

   Commercial mass gainer: £2 to £4 per serving for 600 to 1,250 kcal.

2. 2

   DIY (30g whey, 100g oats, 1 tbsp peanut butter): roughly £1 to £1.50 per serving for around 700 kcal.

1. 1

   Protein per 100g. Anything below 15g per 100g is mostly carbs with a sprinkle of protein. 20 to 30g per 100g is mid pack, and 35 to 42g per 100g is the lean mass gainer tier.

2. 2

   Carbohydrate source. Oat flour and waxy maize digest more slowly and provide steadier energy. Pure maltodextrin spikes blood sugar harder, and cheaper bags tend to lean on maltodextrin.

3. 3

   Fat content. 5 to 10g per serving is normal. Anything above 15g per serving is either MCT-loaded, which is fine but expensive, or padded with cheap oils.

4. 4

   Added creatine. Nice to have at 3 to 5g per serving, but not worth paying a premium for, since a year's supply bought separately costs around £4.

5. 5

   Sugar per serving. Most mass gainers carry 20 to 60g of sugar per serving. That reflects the calorie target rather than a flaw. Lean mass gainer formulas keep this closer to 5 to 15g if a cleaner bulk matters to you.

The fair value comparison for mass gainers is cost per 1,000 kcal, since brands manipulate serving sizes to hit eye-catching numbers on the front of the bag. As of May 2026, Warrior Mass Gainer 5kg costs around £0.52 per 100g and £1.20 per 1,000 kcal, the cheapest credible option. Optimum Nutrition Serious Mass 5.4kg costs around £0.65 per 100g and £1.65 per 1,000 kcal, the best overall value. Applied Nutrition Critical Mass Professional 6kg costs around £0.85 per 100g and £2.10 per 1,000 kcal, a premium justified by its protein density.

Prices rotate weekly. The UK mass gainer comparison table ranks every product by cost per 100g, refreshed weekly across 85+ retailers.