Similac vs. Kirkland Formula

If you are comparing Similac and Kirkland Signature formula, the most important thing to know is this: both meet the same FDA nutritional standards. The FDA regulates all infant formula under 21 CFR 107, which sets minimum and maximum levels for 29 nutrients. Kirkland's formula must pass the same testing and facility inspections as Similac.

Kirkland Signature infant formula is manufactured by Perrigo, the largest store-brand formula producer in the United States. Perrigo also makes Parent's Choice (Walmart), Up & Up (Target), and Member's Mark (Sam's Club). These are not fly-by-night operations — Perrigo produces formula in FDA-inspected facilities using established manufacturing processes.

The real question is not whether Kirkland is safe — it is. The question is whether Similac's proprietary additions (like 2'-FL HMO) are worth the 40–50% price premium. For most healthy, full-term babies, the evidence says probably not.

For a broader look at how formula fits into feeding at every age, see our baby feeding chart.

There are two genuine differences worth understanding: the proprietary additions and the fat source.

2'-FL HMO: Similac's headline ingredient

Similac 360 Total Care includes 2'-FL HMO (2'-fucosyllactose), a human milk oligosaccharide that acts as a prebiotic supporting gut health and immune function. This is a real component of breast milk, and early research is promising. However, the evidence that adding isolated HMO to formula produces measurable long-term benefits in healthy babies is still limited — most studies are short-term and manufacturer-funded.

Kirkland's formula does not include HMO. This does not mean it is nutritionally incomplete — it means it lacks one specific bioactive addition that Similac markets heavily.

Fat source: palm olein vs. no palm olein

Kirkland uses palm olein oil in its fat blend. Similac does not, and markets this distinction prominently. Some research suggests palm olein can form calcium soaps in the gut, potentially leading to firmer stools and slightly reduced calcium absorption. A meta-analysis in Food and Nutrition Research found a modest effect on stool consistency. However, no major health organization has recommended against palm olein in infant formula.

If your baby tends toward constipation, the fat source difference may be worth considering. For most babies, it will not be noticeable.

Here is what the formula industry does not advertise: the FDA requires every infant formula sold in the United States to meet identical base nutritional standards. The $15-per-can difference between Similac and Kirkland is not a safety gap — it is a branding gap.

Similac spends hundreds of millions of dollars annually on marketing, hospital distribution contracts, and pediatrician relationships. When you received a Similac sample at the hospital, that was a business deal between Abbott and the hospital — not a clinical recommendation. Kirkland does not have hospital contracts or television commercials. Those costs are not in your can.

The proprietary ingredients Similac adds (2'-FL HMO) represent a small fraction of the overall formulation. The base nutrition — the protein, fat, carbohydrates, vitamins, and minerals that actually feed your baby — is equivalent. The AAP does not recommend name-brand formula over store-brand formula.

None of this means Similac is a bad choice. It is an excellent formula. It means Kirkland is also an excellent formula, and you should not feel guilty about choosing the cheaper option.

Beyond the ingredient label, there are practical differences parents notice.

Taste: Similac and Kirkland taste slightly different. Babies can have a preference, especially if they have been on one brand for weeks. If you are switching, most babies adjust within a few days.

Mixing: Both dissolve reasonably well in room-temperature water. Some parents report Kirkland powder is slightly grainier, though this varies by batch. A formula pitcher or vigorous shaking resolves any clumping.

Packaging: Kirkland comes in larger tubs (34 oz vs. Similac's 20.6 oz), which means fewer trips to the store. The larger format also contributes to the lower per-ounce cost.

Availability: The main trade-off with Kirkland is that you need a Costco membership and access to a Costco store or Costco.com. If your nearest Costco is an hour away, the convenience factor may not work for your family. Similac is available at virtually every grocery store and pharmacy.

If you are doing combination feeding with breast milk and formula, either brand works equally well.

Switching from Similac to Kirkland (or vice versa) should not require a doctor's visit for most healthy babies. However, contact your pediatrician if your baby shows signs of formula intolerance after switching.

Kirkland Signature infant formula meets the same FDA nutritional standards as Similac and costs 40–50% less. The base nutrition is equivalent. The main things you give up are Similac's 2'-FL HMO and the palm-olein-free fat blend — neither of which has been shown to produce meaningfully different outcomes in healthy babies.

Choose Similac if: you want the HMO prebiotic addition, your baby has been doing well on it and you see no reason to switch, you prefer a palm-olein-free formula, or you do not have convenient access to Costco.

Choose Kirkland if: you want to save $60–80 per month without compromising on FDA-regulated nutrition, you have a Costco membership, and your baby has no specific tolerance issues that require a specialty formula.

Either works well if: your baby is healthy, full-term, and growing normally. The AAP does not recommend one over the other.

If you are switching formulas, tracking feeds and symptoms for 1–2 weeks gives you and your pediatrician a clear before-and-after picture. tinylog makes this easy — log feeds, diapers, and fussiness in a few taps and see whether the switch actually made a difference.

For more store-brand comparisons, see our guides on Enfamil vs. Kirkland and cheapest baby formulas. For the name-brand head-to-head, see Enfamil vs. Similac.

• Best Baby Formulas 2026 — An evidence-based guide
• Kirkland vs. Name Brand — Is generic formula really the same
• Cheapest Formulas — Options that meet every nutritional standard

• U.S. Food and Drug Administration. "21 CFR Part 107 — Infant Formula." Code of Federal Regulations.
• American Academy of Pediatrics. "Choosing an Infant Formula." HealthyChildren.org, 2024.
• Alarcon PA, et al. "Effect of individual fatty acids on calcium absorption in infant formulas." Food and Nutrition Research, 2017.
• Marriage BJ, et al. "Infants fed a lower calorie formula with 2'-FL show growth and 2'-FL uptake similar to breastfed infants." Journal of Pediatric Gastroenterology and Nutrition, 2015.
• U.S. FDA. "Infant Formula Guidance Documents and Regulatory Information." fda.gov, 2023.
• Perrigo Company. "Infant Formula Manufacturing." perrigo.com, 2025.

This guide is for informational purposes only and is not a substitute for professional medical advice. Formula recommendations should be discussed with your pediatrician, especially for babies with allergies, reflux, or other medical conditions.