What does 'billion CFU' mean on a probiotic label?

Probiotic labels love big numbers. "20 billion," "40 billion," and so on. Here is what the number means, and how to read it on three real labels.

What CFU stands for

CFU stands for colony-forming units. It is a count of live microorganisms that are able to multiply and form colonies. "Billion" is just 1,000,000,000, so 20 billion CFU is 20,000,000,000 live units.

Two details on the label change how to read the number: the serving it applies to, and the moment it was counted.

Read the serving first

The CFU figure applies to one serving, and servings differ. Here are three of our labels:

• GutBiome 20, $25: a 13-strain probiotic, 317 mg per capsule, with 20 billion CFU at the time of manufacture. The serving is one capsule daily, with 30 capsules per bottle. It is labeled to support digestive and immune health.*
• Probiotic 40 Billion with Prebiotics, $35: four named strains in an 800 mg probiotic blend labeled at 40 billion CFU per two-capsule serving, plus 60 mg of complex marine polysaccharide and 24 mg of fructooligosaccharide. It is labeled to support digestive health and the body's defenses.*
• GutWell, $35: 1 billion CFU of Lactobacillus acidophilus LA85 (10 mg) per two-capsule serving, alongside 200 mg of inulin, 100 mg of a digestive enzyme blend and 1,000 mg of organic apple cider vinegar powder. It promotes digestive health.*

Notice that the 40 billion figure is for two capsules. By the capsule, that works out to 20 billion each, the same per capsule as GutBiome 20. The serving changes the math, so always check the serving size before comparing.

Why "at the time of manufacture"?

The GutBiome 20 and GutWell labels both qualify the count as "at the time of manufacture." Probiotics are living organisms, so the label is telling you when the number was measured. Follow the storage directions on the bottle, which say to keep it in a cool, dry place.

Is a bigger number better?

Not on its own. The CFU count tells you how many live units are listed. It does not tell you which strains they are, and it does not promise a result. That is why we show the strains on each label: GutBiome 20 names all 13, and Probiotic 40 Billion names its four strains, though that label gives only the total for the blend and not each strain's amount.

Talk to your doctor before starting any supplement, especially if you are pregnant, nursing, under 18 or have a medical condition.

Quick questions

How do I take them?

Per the labels, adults take one GutBiome 20 capsule daily with 6-8 oz of water. For Probiotic 40 Billion, take two capsules daily, one during the day and one in the evening, and do not exceed two capsules per day.

Does CFU tell me the product will work for me?

No. It is a count, not a promise. Our labels do not claim a specific result.

Where can I find a good starting point?

Try the 60-second quiz, or see the Daily Digestive Pair and our other bundles.

*These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.