Why Did Material Prices Go Up? Supplier Creep or Market

If you are asking why material prices went up at your supplier, the honest answer is that both explanations are usually true at once, and they are separable. A market increase moves roughly in step with a published index, lands on every customer buying that category, and your rep can name the manufacturer letter behind it. Creep is the part of the increase that has no matching index move, or that exceeds the index by a wide margin, or that shows up on your invoices and not your competitor’s.

The test is not whether prices went up. They did. Producer prices for construction inputs have been climbing hard, and anyone telling you otherwise is not reading the data. The test is whether your increase on your part numbers matches the size and timing of the market move.

This matters because the first reaction most contractors have to the idea of checking invoices is “prices are up everywhere, what is there to check.” That reaction is reasonable and it is also exactly what makes drift invisible. A rising tide is very good cover, and what 6% drift costs a shop each year runs well into five figures at $40,000 a month of material.

The market half is real, and here are the numbers

Start by conceding the ground that should be conceded. The Associated General Contractors reported that in May 2026 the producer price index for inputs to new nonresidential construction rose 1.8% in the month and 8.4% year over year, the largest annual jump since the pandemic. April had already run 1.7% for the month and 6.6% year over year. June eased slightly month over month but still sat 7.1% above a year earlier.

Underneath that headline, the movement is wildly uneven by category. Year over year through May 2026, AGC reported aluminum mill shapes up 48.8%, copper and brass mill shapes up 26.8%, fabricated structural steel up 15.6% and truck transportation up 17.3%. Compare that to the full 2025 calendar year, when the same nonresidential input index rose 3.3% December to December. The pace changed, and it changed by category.

So when your rep says the market moved, the rep is very often correct. The question is by how much, on your specific items.

Look up the index for your own category

The Bureau of Labor Statistics publishes the underlying series free, and they are the same series AGC quotes. Here is where the common contractor categories sat in mid-2026. Every 2026 reading below carries a preliminary (P) flag from BLS and gets revised, so pull the current value before you use it in a conversation.

Your material	BLS series	Jan 2026 to Jun 2026 (P)
Copper fittings, copper mill shapes	Copper and brass mill shapes, WPU102502	747.384 to 803.275, about +7.5%
Steel, strut, rod, angle	Steel mill products, WPU1017	315.369 to 361.439, about +14.6%
PVC and CPVC pipe and fittings	Plastics pipe, WPU07210603, and plastics pipe fittings and unions, WPU07210604	Pipe 171.280 to 182.609 (P), about +6.6%. Fittings 334.420 to 354.724 (P), about +6.1%
Plumbing fittings and trim	Plumbing fixture fittings and trim, WPU1054	451.310 to 453.198, roughly flat
HVAC equipment	Unitary air-conditioners, except air source heat pumps, WPU114802, and heat pumps, WPU11480734	Air-conditioners 280.520 to 297.025 (P) in May 2026, about +5.9%. Heat pumps 146.923 to 141.564 (P), about -3.6%
Ductwork and sheet metal	Sheet metal products, WPU1073	337.053 in Jun 2025 to 353.935 in Jun 2026, about +5.0%

Two notes on that table before you use it. The HVAC row is deliberately two series, because they went opposite ways: air-conditioners up about 6% while heat pumps fell about 4% over the same stretch. Blending them, or reaching for the industry index PCU333415333415 that averages the whole category together, buries exactly the move you are trying to see. And WPU114802 publishes about a month behind the rest, so its most recent reading here is May 2026 where every other row is June. Match the months before you compare.

Look at the plumbing fittings and trim row for a second, because it is the most useful one on this page. Plumbing fittings and trim held essentially flat from March through June 2026 while steel ran up almost 15% in six months. If your plumbing fittings jumped 18% over that stretch, “the market” is not the explanation, and you now have a specific, checkable thing to ask about rather than a vague sense that things cost more.

That is the entire technique. Not “are prices up,” but “did my price move more than its own index.”

The four tests

Run these against a specific part number, not against your overall spend. Overall spend mixes categories and hides everything.

1. The index test

Take one part you buy repeatedly. Pull your unit price twelve months ago and your unit price now. Compute the percentage change. Compare it to the change in the governing index over the same months.

Your move is within a few points of the index: that is the market. Accept it and move on.
Your move is meaningfully larger than the index: something else is in there. Could be a margin change, a lapsed agreement, a lost special price, or a substituted part number.
Your move is larger than the index and the index went down: that is the clearest signal you will get.

You need your own price history to run this at all, which is why building a unit price history from twelve months of invoices is the prerequisite for every other test here.

2. The breadth test

A real market increase hits a category, not a part. If copper moved, your copper fittings, your copper tube and your copper wire all moved together, in the same direction, on a similar timeline.

If exactly one part number in a category jumped and its neighbors did not, that is not a commodity move. That is a record: an agreement that expired on that SKU, a special price authorization that ran out, a manufacturer substitution. Manufacturer special pricing is negotiated per product and per customer, and is static rather than dynamic, which is precisely why it disappears on one part while its neighbors are unaffected.

3. The notice test

Real market increases arrive with paper. Manufacturers send price increase letters, distributors forward them, and reps mention them because it is the easiest conversation they have all week: “everybody’s copper is up, here’s the letter.”

Ask directly: “Was there a manufacturer price increase on this line? Can you forward the letter?” A yes with a letter closes the question. A yes with no letter and no effective date is worth a follow-up, and the script for a price that moved without notice picks up from there. This is a normal question, it is not an accusation, and reps field it constantly.

4. The consistency test

This one catches the largest single category of non-market increases, and it has nothing to do with commodities.

Same part, same week, two different prices depending on how you bought it. Delivered order at one price, will-call ticket at another. Your usual branch at one price, the branch across town at another. An apprentice’s pickup at one price, yours at another.

A market move cannot do that. A pricing lookup can, and does. Your negotiated rate is attached to a join between your account, the part number and the branch, and breaking any one of the three drops you to a default. The full mechanism is in contract price versus counter price.

Market increase versus drift, side by side

Signal	Real market increase	Drift
Timing	Aligns with an index move and a stated effective date	Appears mid-month, no effective date
Breadth	Whole category moves together	One part number moves, neighbors do not
Direction	Follows the index down as well as up	Ratchets up, rarely comes back down
Paper	Manufacturer letter exists	Nothing to forward
Consistency	Same price on every ticket that week	Varies by branch, ticket type or who bought it
Size	Roughly index-sized	Well above the index
Reversibility	Not reversible, it is the market	Usually correctable, if the invoice is fresh

The bottom-right cell is the reason any of this is worth your Thursday evening. You cannot get copper back to last year’s price. You can get a lapsed agreement reloaded and a fresh invoice corrected, and the window for that is short: see why credit requests get honored on fresh invoices and denied on old ones.

The squeeze runs both directions

Worth saying plainly, because a post like this reads as adversarial if you skip it.

Your distributor is not comfortably absorbing these moves. AGC’s May 2026 release put contractors’ bid prices up only 3.5% year over year against inputs up 8.4%, and April showed the same gap: bids up 3.6% against inputs up 6.6%. That spread is the margin compression running through the whole chain. Distributors are carrying it too, fronting cash on manufacturer rebate claims and filing for reimbursement after the fact.

There is also a mechanical reason increases feel arbitrary that has nothing to do with anyone’s intent. Distributors price off published sheets with columns for several gross profit percentages, plus in-house sheets, customer classification buckets and blanket pricing, and manufacturer special prices layered on top. Trade press describes the habit of marking up on the 5’s and the margin damage distributors take from decentralized purchasing and missed rebate opportunities. That is a lot of moving parts, maintained by people, and parts of it go stale. Most of what you find will be a stale record, not a decision.

Going in with that framing gets you a fixed price. Going in with an accusation gets you a defensive rep and a worse relationship with one of the most valuable counterparties your shop has.

If you are a GC or PM, the same test runs at the sub level

The gap between input costs and bid prices is exactly the pressure that produces escalation claims and change order disputes on your projects. The same discipline applies, one level up.

When a sub comes to you with a material increase, ask which index governs the material and what the index did over the claim period. Standard escalation practice is either index-based (CPI, PPI, ENR) or cost-based on documented actual cost, and contractors are expected to retain initial quotes, bid proposals, purchase orders and invoices to support a claim. ConsensusDocs 200.1, marketed as the only standard material price escalation clause, works by listing the specific impacted materials on a project and adjusting against an agreed objective market index, in both directions. Both directions is the phrase that matters: an index-based clause that only moves one way is not an escalation clause, it is a surcharge.

A sub whose claim tracks its index is telling you the truth. A sub whose claim is triple its index is telling you something else, possibly without realizing it, because they may be passing through their own undetected drift.

What to do this week

Pick your five highest-volume repeat part numbers.
Find your unit price twelve months ago and today for each. Compute the percentage change.
Look up the governing BLS series and compute the same change over the same months.
Flag any part that beat its index by a wide margin.
Run the breadth test on the flagged parts: did the neighbors move too?
Ask your rep for the manufacturer price increase letters on those lines.
Check whether the flagged parts price differently by branch or by ticket type.
Accept the market portion without argument. Chase the rest while the invoices are fresh.

Once you know which increases are real, you can stop arguing about the ones that are and start negotiating the ones that are not. That conversation goes very differently when you bring twelve months of your own unit prices to it: see how to negotiate with your supply house, and what price creep looks like when you finally see it laid out.