4–6 Months: What This Month Costs, What to Buy, What to SkipModel month ~$215/mo model · about 9 diaper changes a day · 28 oz formula/day model (the peak). All prices are model examples — run your real numbers in the simulator.
The appetite peak and the sizing plateau arrive together: formula ounces top out while many babies camp in size 3. This is the quarter where bulk buying finally pays — and where per-ounce formula savings are worth the most money of the whole year.
Model month at 4–6 Months
■ Diapers — $65 ■ Feeding (formula model) — varies by family ■ Wipes & basics — $39
Feeding is shown at a formula-model level for scale; breastfed and combo-fed months sit lower on that segment only. Everything else is stubbornly similar — babies are egalitarian that way.
Buy (this stage earns it)
Move formula to your best per-ounce source now — peak ounces multiply every cent.
Bulk diaper case in the camping size (often size 3) is finally safe.
Start the freezer meal system before solids land next quarter.
Photograph your baby in the cute outfits. Unrelated to money. Do it anyway.
What one day of diapers costs at 4–6 Months, by unit price
Store brand, 17¢$1.53/day
Mid-range, 24¢$2.16/day
Small packs, 35¢$3.15/day
Same stage, same baby — the only variable is the pack you reached for.
Skip (this stage punishes it)
Small-pack diaper habits left over from the newborn fog.
A second expensive 'miracle' sleep gadget before fixing the consumables system.
Stockpiling next sizes 'because they were on sale' — the ceiling still rules.
Your two numbers for this stage
Diaper changes a day: 9 — at a 24¢ model diaper that is $2.16/day, or about $65/month. Keep your real unit price under your written target and this stage is handled. Everything else this quarter is commentary.