Probiotics: compare by cost per billion CFU, not per bottle
Quick answer
Compare probiotics by cost per 10 billion CFU measured at end of shelf life, not price per bottle — and match the strain to your goal, because a bigger CFU count is not automatically a better product.
Alex Soto, Founder, VitaminDB
6 min readUpdated 8/1/2026 NIH-sourced
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Compare probiotics the way you'd compare anything sold by the unit: cost per billion CFU, not price per bottle. CFU (colony-forming units) is the count of live organisms per serving, and it's the number that actually varies between a $12 bottle and a $45 one. But the count is only half the story — the specific strain matters as much as how many, and a bigger CFU number is not automatically a better product.
We sell nothing. We rank probiotics by cost per dose, and this page explains the two label numbers worth reading before you pay.
What CFU means
CFU stands for colony-forming units — an estimate of how many live, viable microorganisms are in each serving. Products on the shelf run from around 1 billion CFU to 100 billion CFU or more per serving, a hundredfold spread. Because that range is so wide, price per bottle tells you almost nothing: a cheap bottle at 1 billion CFU and a pricier one at 50 billion aren't the same purchase, even if they sit on the same shelf.
More CFU is not automatically better
A common assumption is that a higher CFU count means a stronger, better probiotic. That's not how the research reads. Effects are strain- and condition-specific — a strain studied for one use is not interchangeable with another, and the helpful amount depends on the strain and the goal, not on hitting the biggest number in the aisle.
That's why the label detail that matters most is the strain identity, usually written as three parts:
- Genus — for example, Lactobacillus
- Species — for example, rhamnosus
- Strain code — for example, GG
A product that names the full genus, species, and strain is telling you what was actually studied. One that only says "probiotic blend, 50 billion CFU" is selling you a number without telling you what's inside.
"At manufacture" vs "at expiration" — read the honest number
Live organisms die off over time, so CFU counts drop between the day a product is made and the day you swallow it. Labels handle this two ways:
- CFU at time of manufacture — the count when it left the factory, which is higher than what you actually get.
- CFU at expiration (or "through end of shelf life") — the count guaranteed at the end of the date on the bottle.
The end-of-shelf-life number is the honest one, because it's what you're guaranteed to receive rather than a peak you already missed. A "100 billion at manufacture" product can deliver far fewer by the time you take it; a "30 billion through expiration" product tells you the floor. When two labels use different bases, they aren't comparable until you convert them to the same one.
Shelf-stable vs refrigerated
Both formats exist and both can be legitimate. Refrigerated products rely on the cold chain to keep organisms alive; shelf-stable products are formulated (and often blister-packed) to survive room temperature. Neither is automatically superior — what matters is the guaranteed CFU at expiration under the storage the product is designed for. If you buy refrigerated, keep it cold; if you buy shelf-stable, the expiration count already assumes a room-temperature shelf.
How to compare cost per 10 billion CFU
Once you're reading the right numbers, value is simple arithmetic. Pick a common yardstick — cost per 10 billion CFU works well across the range:
- Use the CFU at expiration, not at manufacture.
- Cost per serving = bottle price ÷ servings per container.
- Cost per 10 billion CFU = cost per serving ÷ (CFU per serving in billions ÷ 10).
- Then confirm the strain matches what you're buying it for.
That last step is the guardrail: compare on cost per CFU only among products with the strain you actually want, not across unrelated strains. A lower cost per CFU is no bargain if it's the wrong organism.
Our best probiotics by cost per dose page ranks products cheapest-first; browse listings on the probiotics nutrient page, and see exactly how we normalize CFU and servings in our methodology.
Bottom line
- Compare cost per billion CFU, not price per bottle.
- More CFU isn't automatically better — the strain (genus, species, strain code) matters as much as the count.
- Use the CFU at expiration, not at manufacture — it's the guaranteed number.
- Both shelf-stable and refrigerated can be fine; store them as designed.
Match the strain to your goal first, then buy the cheapest cost per 10 billion CFU. This is general information, not medical advice.
Covered nutrients: probiotics
See the live cost-per-dose data
This guide is editorial — the prices below are real and current.
Frequently asked questions
How many CFU do I need?
There is no single right number, because effects are strain- and condition-specific — the useful amount depends on which strain you are taking and why, not on hitting the biggest count. Products range from about 1 billion to 100 billion CFU or more per serving. Pick a strain studied for your goal and follow its labeled serving rather than chasing a high number. This is general information, not medical advice.
Is more CFU better?
Not automatically. A higher CFU count is not the same as a more effective product, because what a probiotic does depends on the specific strain and the condition it was studied for. A large count of the wrong strain is not more useful than a smaller count of the right one. Not medical advice.
What should I look for on the label?
Two things: the full strain identity (genus, species, and strain code, such as Lactobacillus rhamnosus GG) and the CFU counted at expiration rather than at manufacture. The strain tells you what was actually studied, and the at-expiration count is the amount you are guaranteed to receive at the end of the bottle's shelf life.
How do I compare cost between probiotics?
Use the CFU at expiration, divide the bottle price by servings to get cost per serving, then divide by the CFU per serving to get a cost per billion (or per 10 billion) CFU. Only compare that figure among products with the strain you actually want — a lower cost per CFU is no bargain if it is the wrong strain.
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