The letter says 5% but the list says otherwise on many lines

That is the normal case. The percentage in a letter is an average or a headline, and the price list is the contract. Compare the two lists by item code and the lines above the announced figure are the ones to raise with the supplier.

An invoice after the effective date must be checked against the new list

That is what the service does: the list in force on the invoice date is the reference. Where the supplier's terms protect orders placed before the notice or effective date, the reply still shows every line billed above the old list as a difference, and the order date is your argument for the old price.

Pack-size changes are visible on the invoice

They are not. Invoices in the chains we have read print code, description, quantity and price, not the pack content. A smaller pack at the same price shows only when two versions of the price list are compared line by line.

A digest is slower than a reply per document

It is slower on purpose. A list-to-list comparison and a price drift across invoices are invisible in a single document, so the service confirms receipt at once and sends the substantive email when the set is complete, with a count of what it compared and what it could not read.

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Check a supplier price increase

Tarkistettu viimeksi 7 September 2026 · Tämä sivu on saatavilla englanniksi.

To check a supplier price increase, compare the new price list with the previous one by item code, not the letter that announced a percentage. Then compare the first invoices after the effective date with the new list. Price Double Check does both by email: forward both price lists and each invoice, and the lines that moved come back.

A price increase arrives as two documents that do not say the same thing. The letter says "prices rise by 5% from 1 October". The price list attached to it, or sent a week later, carries the actual figures per item code. In the chains we have read, the average in the letter and the lines in the list agree only on average: some codes rise by 2%, some by 12%, a few fall, and a few keep their price while the pack behind the code gets smaller. The increase you will actually pay is the one in the list, weighted by what you buy, and the only way to know it is to put the two lists side by side.

The letter announces, the price list is the increase

Suppliers announce increases in a fairly standard way. Distribution agreements usually require written notice ahead of the effective date; sample clauses collected by Law Insider put the notice at 30 days in some contracts and 60 days in others, and require the notice to state the current price, the increased price and the effective date. Guides for sellers writing such letters recommend 30 days for small accounts and 60 to 90 days for business customers with annual contracts. What lands in your inbox is therefore a letter with a headline figure, an effective date, and sometimes a promise that orders placed before that date are billed at the old price.

The headline figure is not a finding. If the supplier says 5% and the list says 5% on every line, there is nothing to report. The finding is the composition the letter does not disclose: which codes moved more than announced, which moved in the other direction, and which kept their price at a smaller pack size. That composition is visible only line by line, and only against the previous list, because a single price list on its own has nothing to differ from.

Effective dates and price protection decide which list applies

Every invoice must be checked against the list in force on the date that governs the price, and that date is not always the invoice date. Three clauses appear again and again in supplier terms and letters, and each one moves the boundary:

Effective date: the new list applies to orders, deliveries or invoices from that day, depending on the wording. A list without a stated effective date takes the date of the email that carried it.
Price protection: sample distributor clauses state that orders placed before the notice date, or before the effective date, are shipped and billed at the prices existing before the increase. An invoice dated after the effective date for an order placed before it should still carry the old prices.
Valid until: some lists carry their own expiry. After that date the supplier can bill anything, and the only check left is against the last list you were sent.

This is why we keep every price list you forward rather than only the latest, and why the date of the covering email matters. When an invoice arrives, the comparison uses the list in force on the invoice date: the one with the latest date on or before it. A list with no date of its own takes the date it reached us. The reply names the list it used, so if the supplier promised price protection on an earlier order and billed the new price anyway, the line shows the delta against the new list, and the order date with the previous list is your argument for the old price.

How to check a supplier price increase, step by step

To check a supplier price increase is to run two comparisons, one week apart. The first is list against list and takes place as soon as the new list arrives. The second is the first invoices against the new list and runs as deliveries come in.

Step	Documents	Joined by	What it shows
1	New price list vs previous	item code	per-line rise, falls, pack changes, codes dropped
2	Letter vs step 1	the announced %	lines above and below the announced figure
3	First invoices vs new list	item code	lines billed at a third price, neither old nor new
4	Invoices before the date vs old list	item code	protected orders billed at the new price

Step 3 is the one buyers skip and the one that costs money. In a chain we validated, a sports-nutrition manufacturer had been billing one code at a price 17.75% above the list in force for months; the newer list that would have justified it had never been sent, and the line ate 91% of the margin of that delivery. A price increase is the moment such gaps appear, because the supplier's own system gets a new price before the buyer's copy of the list does. The full method for one invoice is on compare an invoice with a price list; to check a supplier price increase we run the same join over two lists first.

All of this is by item code, never by description. Of 442 lines we compared in one chain, 335 had a description that differed from the price list wording, and a new price list is exactly where descriptions get rewritten. A join by name would report half the catalogue as new and miss the increases hidden in renamed lines. Codes with suffixes such as 5116_1 are normalised and confirmed by price before they count as the same item.

Pack size shrinks at the same price

The quietest form of a price increase is a pack that shrinks. Trade press on shrinkflation describes it as keeping the visible price point unchanged while reducing the quantity in the pack, and reports that suppliers apply it to wholesale customers as well as to consumers. In our validation chain it happened four times: same code, same price, a smaller unit count or volume in the description of the new list. On the invoice the pack size is not printed at all, so the price check per invoice will never see it. It is visible only between two price lists.

We report it as its own row: code, old pack, new pack, price unchanged, and the price per unit before and after. We do not call it an increase, because the documents do not say whether the supplier changed the pack or corrected an old description; a 550 cc bottle in one list and 600 ml in the next is a difference to show, not to judge. The per-unit figure is yours to take into the conversation.

A negotiation position built from invoiced prices

Advice on responding to a supplier increase, such as the guide published by Planergy, comes down to one thing: take the emotion out and bring the numbers in, using your own price history and cost breakdowns rather than the supplier's average. The numbers that carry weight are the ones you actually paid, not the ones in a list. Two arguments come straight out of the invoices:

Lines already billed above the old list. If the supplier has been charging a higher price for months before announcing an increase, the increase is on top of a rise you never agreed to. In one chain a bar was billed at 1.26 from March against a list price of 1.176, and 1.26 appeared in a price list only in October. The announced increase for that line was already paid.
Weighted increase on what you buy. The letter's 5% is an average over the catalogue. Multiplying each line's rise by the quantities on the last six months of invoices gives the increase on your basket, and the codes that drive it. Those are the lines to negotiate; the rest can be conceded.
Substitutions. A code replaced by a neighbouring one at a higher price, without a note, is an increase that is not in the letter at all. Comparing the purchase order with the invoice is where it shows.

Both a list-to-list comparison and the drift of a price across invoices are delivered as a digest, not as a reply per document: the arrival of each document is confirmed in a line, and the substantive email arrives once, with the complete picture and a statement of coverage such as "14 invoices over 6 months compared, 3 could not be read". Ranking in the price-list digest is by percentage and by novelty, never by money, because a list carries no quantities; money is computed only where invoices exist. The longer-run view is described in track supplier price changes over time.

What the check does not do

It does not decide whether an increase is fair. Commodity trends and the supplier's cost base are your argument to make; we supply the line-level facts.
It does not judge freight, units of measure, or a description that changed alongside the price. These are shown with their amounts and left to you.
It does not report a code missing from a partial list as discontinued. Dropped codes are reported only between two complete catalogues.
It reads the PDF, Excel or CSV attached to the email. It does not read a photograph of a letter and it does not connect to the supplier's portal; why a parser alone is not enough is in parser is not an answer.

The whole check is deterministic. The same two lists give the same table every time, line sums are reconciled with the printed total of every invoice to the cent before any line is compared, and a line the service could not match is listed with its amount rather than silently dropped.

Lyhyesti

The letter says 5% but the list says otherwise on many lines: That is the normal case. The percentage in a letter is an average or a headline, and the price list is the contract. Compare the two lists by item code and the lines above the announced figure are the ones to raise with the supplier.
An invoice after the effective date must be checked against the new list: That is what the service does: the list in force on the invoice date is the reference. Where the supplier's terms protect orders placed before the notice or effective date, the reply still shows every line billed above the old list as a difference, and the order date is your argument for the old price.
Pack-size changes are visible on the invoice: They are not. Invoices in the chains we have read print code, description, quantity and price, not the pack content. A smaller pack at the same price shows only when two versions of the price list are compared line by line.
A digest is slower than a reply per document: It is slower on purpose. A list-to-list comparison and a price drift across invoices are invisible in a single document, so the service confirms receipt at once and sends the substantive email when the set is complete, with a count of what it compared and what it could not read.

Forward one invoice and the price list to your address, then the new price list when it comes, and the lines that moved arrive as a table.