Nappy (Diaper) & Formula Cost Calculator

Understanding the nappy and formula cost calculator — concept and principle

Nappies (diapers) and infant formula are two of the largest everyday costs in a baby's first year. This calculator estimates the monthly spend on each from your daily use, the price per nappy, and your formula tin's price, weight and scoop size, and shows how many tins you will get through each month so you can plan purchases and compare brands or pack sizes.

Nappies cost $42.56 and formula about 4.46 tins ($53.50) in an average month.

How it is calculated

Nappies per month = nappies per day × 30.4 × price per nappy.
Powder per day (g) = formula per day (mL) ÷ 30 × scoop powder per 30 mL (g).
Tins per month = powder per day × 30.4 ÷ tin weight (g).
Formula per month = tins per month × tin price.

30.4 is the average number of days in a month (365 ÷ 12 ≈ 30.4).

The principle

Both costs are a daily quantity multiplied by a unit price and by the days in a month. For formula, the label tells you how much powder to add to a given volume of water, so the daily volume fixes the daily grams of powder. Dividing monthly grams by the tin's net weight gives tins, and tins times price gives the cost. The calculator keeps fractional tins, which reflects the average cost; in practice you buy whole tins, so stock should be rounded up.

Worked example

Inputs: 7 nappies a day at $0.20; 800 mL formula a day; tin $12, 800 g; 4.4 g powder per 30 mL.
Nappies: 7 × 30.4 × 0.20 = $42.56 per month.
Powder per day: 800 ÷ 30 × 4.4 = 117.33 g.
Per month: 117.33 × 30.4 = 3,566.9 g; ÷ 800 = 4.46 tins.
Formula cost: 4.4587 × 12 = $53.50 per month.

Each point is the calculator re-run with only “Nappies per day” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Nappies per day	Nappies per month
1.75	$10.64
3.5	$21.28
5.25	$31.92
7	$42.56
8.75	$53.20
10.5	$63.84
14	$85.12

How to read the result

Daily nappy use is highest in the newborn weeks and falls as the baby grows, while formula volume rises over the first months and then changes again when solid foods start, so rerun the calculation every few months. Buying larger packs or tins usually lowers the unit price; compare by price per nappy and price per gram, not by pack price.

Common mistakes

Using another brand's scoop weight; scoop sizes and powder-to-water ratios differ.
Entering prepared feed volume from a different stage of formula.
Forgetting wipes, nappy cream and bottles, which add to the monthly total.
Rounding tins down and running out between shopping trips.

Keep in mind: Always prepare formula exactly as the manufacturer's label and your health professional advise; never add extra powder or water to stretch a tin. Feeding amounts here are inputs for budgeting only, not feeding advice.

Frequently asked questions

Why 30.4 days per month?

It is the average length of a month over a year, so twelve monthly figures add up to a full year.

Are reusable nappies cheaper?

Often over time, but count washing, energy and the upfront set cost before comparing with disposables.

Is ready-to-feed formula more expensive?

Generally yes per millilitre; enter its price per mL-equivalent to compare fairly.

Sources: World Health Organization — Safe preparation, storage and handling of powdered infant formula: guidelines (2007) · NHS — How to make up baby formula

Checked 8 Nov 2026. Typical coverage rates and standard formulas. Always check the product label and local building rules; buy 5–10% extra for waste.

Your numbers