Estimate the cost of baby gear essentials.
Baby gear is four large categories and a discount rate. Summing the categories gives the retail exposure; the second-hand share is what most families actually apply to it, since cribs, clothing and strollers all hold up well used and much of the list arrives as gifts. The important exception is the car seat: it should be bought new because its crash history is unverifiable second-hand and the plastics degrade, so exclude it from the discounted share if you are modelling carefully.
Net baby gear cost
Net = (stroller and car seat + crib + feeding + clothing) x (1 - second-hand share)
Cost planning figures only. Car seats, cribs and sleep equipment are subject to safety standards that vary by country; check current regulations and manufacturer guidance, and do not use a second-hand car seat of unknown history.
Car seats and crib mattresses. A used seat may have been in a collision that leaves no visible damage, and mattress firmness and hygiene both matter for safe sleep. Everything else on the list is generally fine used.
For a first baby, often a quarter to a half of the clothing and feeding categories, and rarely the large items. Setting the second-hand share around 25% across the whole list is a realistic planning figure.
Usually a little against buying a stroller and infant seat separately, but it locks you into one brand's upgrade path. The saving is real but smaller than the marketing implies.