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Methodology

How we count proven savings

"Proven" means proven with your own till receipts. Only code computes the amounts, by the rules below — never AI and never a typed number.

Version 2027-01

What counts

Proven

Proven with your own till receipts by the rules below. Counted, and can feed the dream fund.

Likely prevented

A separate number, always labelled "likely". Never added to "Proven". Comes in a later version.

Does not count

Everything else — analysis only.

The rule "same product, lower price"

  1. 1Only receipts signed by the server

    When you photograph a till receipt, the server reads the QR code from the photo itself and signs its date, total and lines. Expenses typed by hand never take part. Your browser checks the signature before using the receipt.

  2. 2Your usual price

    For each product we look at your receipts from the 90 days before the purchase — at least 3 different receipts. The usual price is their middle value (for an even count, the lower of the two middle ones). We compare the price per kilogram, litre or piece, so different pack sizes are compared fairly.

  3. 3The saving

    Saved = (usual price − price paid) × quantity. Purchases above the usual price in the same month are subtracted, so ordinary price swings never turn into a "saving". Every scanned purchase of the product is subtracted — also receipts you edited, discarded or whose expense you deleted, and also when they were scanned earlier than older receipts. A saving counts only against receipts scanned before the purchase. A receipt entered without proof neither adds nor subtracts. Line prices are read from the photo; so we count only receipts whose lines add up to the QR total (within 1 cent).

  4. 4Too good to be true

    If the price is below half of the usual one, it counts only when another of your receipts within 30 days shows the same price (up to 5% higher). Below a third, it never counts automatically — it stays "to check".

  5. 5Quantity and monthly caps

    We count a quantity up to 2 times your usual quantity — stocking up is not saving. Proven savings per household are capped at €300 a month; above that the card goes "to check" and is not counted.

What the calculation looks like

Example

Three receipts for coffee at €7.20, €7.40 and €7.60 — the usual price is €7.40. The next receipt is €5.90:

(€7.40 − €5.90) × 1 = €1.50

Every proof card shows exactly this formula with your numbers and the receipts they come from.

What never counts

  • Fresh produce sold by weight (fruit, vegetables).
  • Storno receipts, receipts in leva from before 2026 and receipts without a valid QR code.
  • Photos of a screen, and receipts where the QR total or number differs from the printed one (or the printed number cannot be read).
  • Comparisons between different products ("substitutes") — not counted in this version.
  • Lines with unrealistic prices (over €1,000 per kilogram, litre or piece, or over €5,000 per line).
  • "You spent less this month", avoided fees and instalments, offers.
  • Amounts suggested by AI, and amounts typed by hand.
  • Bills received by e-mail: the comparison with earlier months ("higher usage" or "higher price") is analysis, not a saving.

Why AI never computes amounts

AI only reads the receipt. The numbers are checked against the QR code and signed, and the saving is computed by code that is the same for everyone and described here.

What we check

The signature, that the QR code matches what was read, the sum of the lines and whether the receipt was already entered — in your account or another. Receipts are not checked with the tax agency (NRA).

If you disagree

Every card has an "I disagree" button. The amount leaves every counter at once, even offline. We look into it; if the calculation is right, you decide whether to put it back. Disagreeing never counts against you.

Offers by e-mail

  • We read only newsletters on your offers address that are signed by the chain's own verified mail. Everything else is listed under "Other" with the reason.
  • Offers are read on your device by rules. Only on VIP and with AI consent is the text of a newsletter the rules cannot read sent, without addresses, names or links; we accept only prices that appear word for word in the e-mail.
  • We show an offer only if you need the product, if it is at least 10% below the lower median of at least 2 of your scanned receipts in 90 days (below a third of it we do not show it), and if you will use it before it spoils. We never compare a different brand without asking you. Basic plan: up to 3 chains, which you can change once per calendar month.
  • Wishes (VIP): the chain sells such things, a word of the wish is in the product, the size is the same and the price is no more than the maximum you set.
  • Weekly plan (VIP, Thursday): a second or third shop only if the difference is at least €5; we show an "expected difference", never "saved".
  • An offer is never a saving and never enters the counters, the dream fund or reports. If a signed receipt shows you bought the product on the offer (same chain, within the dates, at a price up to 2% above the offer), the proven saving's card only notes "bought on an offer" — the amount is computed by the same rules.

How a report is verified

A household can publish the proven amount of a finished month as a code HW-XXXX-XXXX. The server does not take the app's number: it checks every receipt against what it signed itself, requires every receipt of the 90 days before the month, the month and the 30 days after it and computes the amount itself by the rules on this page. Its amount is published — never more than the app showed.

  • Above €100 for the month, above 15% of the spending on receipts with a QR code, or a card above €30 — a person reviews the code first ("In review"). Without a review within 14 days it becomes "Not confirmed".
  • Statuses: "Valid", "In review", "Not confirmed", "Replaced by a newer code", "Withdrawn by the household", "Withdrawn after a check". The amount is shown only while the code is valid.
  • Disputing an amount, or editing or discarding a receipt it used, withdraws the code at once.
  • A code proves the receipts photographed up to the day of publication. A receipt that was never photographed — or photographed but cancelled before it was saved — takes no part: neither in the saving nor in the usual price. A receipt saved and later discarded does take part (it can only lower the amount). Receipts are not checked with the tax agency (NRA).

Check a code

What the server learns

  • Briefly: the numbers from reading the receipt, so it can sign them.
  • Keeps: an irreversible fingerprint of the receipt (so it cannot be entered twice, also in another account) — 400 days, also after the account is deleted.
  • Keeps: the receipt's date, when it was scanned, whether it can be evidence, and a fingerprint of the signed data.
  • Keeps per receipt: its state (waiting to be saved, saved, edited, discarded, expired, replaced) and why it changed (e.g. "total edited", "receipt discarded", "revoked by an administrator"), and what stops it from being evidence (e.g. "photo of a screen", "storno").
  • For a dispute ("I disagree"): the disputed amount, which receipts (signature ids) are involved, the reason and the dispute's status.
  • If you publish a code: briefly the signed facts of the receipts of the 90 days before the month, the month and the 30 days after it (the same the server already signed), so it computes the amount itself. Keeps: the month, the amount, the number of receipts and shops, which receipts and cards were used — while the code can be checked (without the household after it is deleted).
  • Trust index (never shown, never used for marketing): only repeating patterns — e.g. receipts entered before in several other households, or many receipts with "instructions to the AI" from different shops. Kept up to 400 days; the details of single cases — 30 days.
  • E-mail for bills: e-mails pass through Cloudflare and our code there unencrypted and are encrypted with the household key at once; Cloudflare's log shows the sender, recipient, subject and time. The server keeps only the encrypted e-mail until it is processed (at most 30 days), its size, the time it arrived and whether it is for bills or offers.
  • Does not keep: product or shop names, receipt or line amounts, your counters, undisputed saving amounts or your goals.

Details: Privacy policy

Methodology version 2027-01.