Methodology: how we measure prices
This page explains where the numbers on each product page come from, how often we take them and what exactly they mean. If anything we publish does not match what it says here, that is our mistake and we want to hear about it.
What we measure, and how often
Once a day we take the price of every product at every shop that lists it and store it with its date. We never delete points or correct the series retroactively: whatever we recorded on a given day stays as recorded, even if it later turns out to have been a one-hour promotion.
We currently track 181 products across 5 categories, with 14,467 price observations recorded. The median series is 94 days long; the longest is 104.
Sources
Prices come from the official catalogues of the affiliate networks we work with: AliExpress, Kaspersky - ES. We do not scrape shop websites and we do not copy prices from other comparison sites.
The price we show is the shop’s price at the time of our last reading, with that date visible on the page. If the reading is more than 14 days old we stop asserting it as structured data: we still display it, but we do not ask Google to publish it as a live offer.
What each figure means
- Lowest recorded price
- The lowest price we have seen since we started tracking that product, with its date. We do not say “all-time low” until we have 90 days of history: before that the page says “lowest in N days”, which is what we actually know.
- 30 / 90 / 365-day average
- Arithmetic mean of the prices recorded in that window. If the series is shorter than the window, we average what we have; the yearly average is only shown from 180 days of history.
- Percentile of the current price
- What share of recorded days had a price lower than today’s. 20% means today’s price sits in the most expensive 20% of its own history. It is the number that best answers “is this cheap?”, because it does not depend on discounts announced by the shop.
- Significant change
- A move of at least 5% from the last price we already counted as a change. The threshold is not arbitrary: in this catalogue the median daily change is 0% and the 75th percentile is 0.48%, while the 90th percentile jumps to 8.24%. Either it does not move or it really moves; 5% falls in the gap. Counting currency-conversion cents as a “price change” would only add noise.
- Typical variation
- Median of the absolute daily change. It tells you whether the price is steady or jumpy.
- Price signal
- “Good price”, “Normal price”, “Expensive now” or “Too little data”. It comes only from comparing today’s price with its own history: at its low or at least 10% below its 90-day average is a good price; 8% or more above it, expensive. It is not a rating of the product — we don’t test them — and until October 2026 it was a 1-to-5 score that we withdrew because it looked like a review without being one.
- Struck-through “was” price
- We only show it when the series is at least a week long and that “was” price is no more than 5% above the highest price we have seen charged. Many stores advertise a list price the product has never had; repeating it next to our price would endorse a shop-window discount.
When we assert nothing
We need at least 7 days of history before a page talks about lows and averages. Below that we say we have just started tracking the product, because an “all-time low” based on three days of data means nothing.
For the same reason, a product page is not offered to search engines (it carries “noindex”) until it has 14 days of history, and neither is the “cheapest” list of a category with fewer than 10 products: it would be the same page as the category.
Our relationship with the shops
We earn a commission if you buy through our links, at no extra cost to you. That does not change the price we show or the order the shops appear in: we always highlight the lowest real price we have read. We also do not accept payment to include a product or to change its price signal, which comes from a formula rather than an editorial decision anyway.
Links to shops carry rel="sponsored nofollow" and go through a redirector we do not index, so it is clear to anyone — reader or search engine — which links are commercial.
Mistakes
A feed can carry a wrong price, the wrong currency or a product that no longer exists. When we spot it we correct the data going forward and leave the past series untouched. If you see something that does not add up, write to [email protected].
By Carlos Marcos · updated 26 October 2026