How does this all work?
Short answers to the questions that matter most — where prices come from, how the savings are calculated, and what we deliberately leave out.
Where do the prices come from?
Woolworths and Coles via the same product JSON their own websites use, and Amazon AU via the official Product Advertising API. No third-party data partners, no community-curated price lists.
How often are prices refreshed?
Every 24 hours. The "Refreshed N hours ago" stamp on the dashboard reflects the most recent successful run. Individual products show their own "Last checked" line on the comparison page.
How is the saving calculated?
Each product is normalised to a per-unit cost (per pill, per nappy, per 100 mL, per load, etc.) so two pack sizes compare apples-to-apples. Monthly saving = per-unit gap × your assumed monthly usage. With a household profile we scale usage to your home; without one we use a 2-adult national-average.
How does Subscribe & Save factor in?
Where Amazon advertises a Subscribe & Save discount we apply it to the saver price and label the row "S&S X%". Prime members get a boosted 15% tier on nappies and wipes. If your profile says you don't have Prime, the calculator allocates the $79/year subscription cost upfront and adjusts the payback timeline.
What's not included?
- Aldi — no online prices to track day-to-day. The Aldi comparison article uses manually-collected pricing instead.
- Cashback / loyalty points — Cashrewards shut down in October 2025, and points programs are valued differently by every household, so we leave that maths to you.
- Half-price specials — too transient. We show everyday shelf price, which is what recurring purchases actually cost.
Do you store my household profile?
No. Your profile lives in your browser's localStorage and is sent to the server only to compute personalised numbers — never persisted, never tied to an account (there are no accounts), never used for advertising. Click logs record only the destination ASIN and which placement on the page sent you, never anything that identifies you.
How do you make money?
"Buy on Amazon" buttons are Amazon Associates affiliate links — if you buy through one, Amazon pays us a small commission and your price is unchanged. Many products in our catalogue actually pay 0% commission (Amazon excludes whole categories like nappies and grocery staples from its associates program), so they're recommended on price alone. When the cheapest option is at Coles or Woolies, we say so; recommendations aren't influenced by which products are affiliate-friendly.
I think a price is wrong. What do I do?
Check the per-product "Last checked" line on the comparison page first — sometimes a single retailer's endpoint failed on the most recent refresh. If the figure still looks off, please flag it via the Contact page.