Buying rules — Stop the leaks once
After the calculators and databases, this page is the immune system. Every trap below works by making a tired parent compare the wrong numbers, at the wrong moment, under time pressure. Each comes with its rule — short enough to remember at 2 a.m., which is when it will be needed.
Bulk cases feel like virtue. But a diaper outgrown is a 100% loss, and in the fast sizes babies outgrow on a schedule measured in weeks. We worked the full math in the diaper guide: stockpiling 800 diapers to save 5¢ each can net lose $50 when 300 go unworn. Rule: two weeks in fast sizes, six weeks in camping sizes, existing stock always counted.
Percentages are computed from prices you never agreed to. Forty percent off a premium brand routinely loses to full price at a store brand, in unit terms. Rule: never buy a percentage. Buy a unit price, compared against your written target.
The loudest number on the shelf was the worst price on the shelf. This happens weekly, in every category, by design.
Registries are built to expand: suggested items, completion anxiety, and the feeling that a missing gadget is a missing piece of readiness. Typical drift adds wipe warmers, specialty pillows, bottle machines duplicating the dishwasher, and three kinds of swaddle for a baby whose preferences are unknowable. Rule: register consumables and the boring basics generously; register gadgets only after the minutes-math in our gear guide approves them; and use the completion discount on a short, pre-written list — not a browsing session.
Convenience packs at convenience prices, bought one emergency at a time, are the most expensive supply system in babyhood — 30–100% unit premiums, repeated 100+ times. Rule: one standing source (subscription or monthly bulk run) plus a two-week buffer. Emergencies should be rare because the system, not your memory, does the remembering.
Wipes, creams, detergents and bags each drift a tier upward under marketing pressure, a dollar here, three there — until "miscellaneous" is $60 a month and nobody can say why. Rule: name your five consumable lines with model prices (our wipes guide shows the five) and re-price them twice a year, like a landlord reviewing leases.
Four questions, ten seconds, most traps disarmed. Print them inside the pantry door.