Is Costco worth it if milk and eggs are my main purchases?

Usually, no — Costco is probably not worth it if milk and eggs are your main purchases.

A basic Costco membership is about $65/year in the U.S., so you need to save roughly $5.50/month just to break even. Milk and eggs can be cheaper at Costco, but the per-trip savings are often too small unless your household uses a lot and can finish bulk quantities before they spoil.

Rule of thumb:

• Worth it: you buy several gallons of milk and multiple dozens of eggs every month, and Costco is already on your normal route.
• Not worth it: you buy 1 gallon of milk and 1 dozen eggs per week or less, especially if you make extra trips just for them.
• Better test: compare your local Costco unit price against Aldi, Walmart, Target, Kroger, or your local grocery store for 3–4 weeks. If the monthly savings are under about $6, the membership doesn’t pay for itself on milk and eggs alone.

Costco becomes much easier to justify if you also buy gas, rotisserie chicken, paper goods, pharmacy items, meat, coffee, diapers, pet food, or occasional big-ticket items.