Best Mass Gainer UK: Best Options Compared for 2026

Applied Nutrition Critical Mass Professional wins for its stronger protein density and tested-sport option. Warrior Mass Gainer wins strict value. Serious Mass is the familiar high-calorie choice, but its giant manufacturer serving can disguise an expensive and difficult-to-drink dose; compare matched calories and protein instead.

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.

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.