Cash flow

The cost error that changes what you buy

A cost price that is too low does not break the arithmetic behind an order quantity. It breaks the judgement sitting on top of it, and that is where the buying decision really happens.

Marcus VolstedCo-founder, Restocio Published 11 September 2026Updated 11 September 20267 min read

The cost error that changes what you buy

Does a wrong cost price change how much you should order?

No. The quantity comes from your sales rate, your lead time, the coverage you chose and what is already on the shelf or on the water. A cost that is too low leaves that arithmetic untouched. What it moves is the price tag on the answer, and the price tag is the thing you actually approve.

The first half of this gets written constantly. A cost missing freight and duty overstates your margin, which is true, and it has its own page here along with a hundred elsewhere. What the same error does to purchasing almost never gets written. How much cash you believe an order needs, which line looks expensive beside which, what you quietly drop when the total comes back bigger than the month allows.

The gap on one order line

Say the gap on one of your imported lines is 22 per cent. That is not a benchmark and nobody can hand you a trustworthy one, but it is the right order of magnitude for a cost field holding the supplier invoice and nothing else, and the ten-minute audit gets you your own number instead of borrowing this one. Put it against a purchase plan.

A line recommends 600 units. Cost per item says 14.00, so the plan prints 8,400. If the real landed cost is 22 per cent higher, 17.08, those same 600 units cost 10,248. The quantity was right both times. The budget it got approved against was short by 1,848 on one line.

Nothing in there is a forecasting failure. Demand was read correctly, the lead time was right, the deadline was honest. The only broken input was a number typed once when the product was created, and it never touched the units.

What the cost error moves, and what it leaves alone

Precision matters more than drama here, because the two halves call for different fixes.

What	Does an understated cost move it?	Why
The recommended quantity	No	Sales rate, lead time, coverage, stock on hand and units already inbound. No price is an input to any of them.
The order deadline	No	Days of stock minus lead time minus a safety margin. Also cost-free.
Which products show up as needing an order	No	A row appears because it is running out, not because of what it earns.
What the plan says it will cost	Yes, by the same percentage	It is recommended units multiplied by the cost you registered.
Margin per unit, and whether flying part of an order in pays for itself	Yes	Both are computed from that cost, so both read kinder than reality.
Where a line sits in a list ranked by spend	Yes	An understated line looks cheap and sinks down a list sorted by purchase value.
What you approve, stage or trim	Yes, and this is the expensive one	You are deciding on the money, not on the units.

Why does an understated cost make you buy more?

Because cheap-looking stock gets approved whole. A plan that prints 8,400 goes through without much argument. The same plan at its real 10,248 gets staged across two orders, or trimmed to the lines under genuine time pressure, or funded by pushing something else out a month. The units were never the decision. The total was.

Then the difference turns up at the bank rather than in any report, weeks later, with nothing to point at. That is the quiet version of profitable on paper, empty at the bank, and it deserves separating from the ordinary cash lag of importing. Lag is structural and you can plan around it. This is a typo compounding every time you reorder.

Which lines get cut when the number is wrong?

The wrong ones, and not at random. Understatement is largest exactly where freight is largest: imported, bulky, anything that had to be flown in to cover a gap. A domestic line whose cost was already complete looks expensive beside an import whose freight is missing from the figure, so the domestic line gets trimmed first.

Put that 600 unit import at a typed 14.00 next to a 400 unit domestic buy at a complete 22.00. The typed numbers say 8,400 against 8,800, so the domestic line is the bigger commitment and the obvious thing to cut. On real costs it is 10,248 against 8,800 and the ranking flips. This error is not noise spread evenly across a catalogue. It leans the same way, on the same products, every quarter.

How do you get your own number before the next approval?

Rebuilding one SKU's real cost from its invoices is a ten-minute job and it is written up here, so it is not repeated. The step that belongs to this page is the one after it: take the percentage gap the audit gives you, apply it to the total on the plan you are about to approve, and read the second figure instead of the first. That is the money actually leaving.

Do it on the import lines before the domestic ones. And expect the gap to widen rather than hold, because the cost field sits still while freight rates and supplier prices do not, which is a second failure stacked on the first.

How Restocio handles it

Two deliberate separations, both checkable if you use the app.

The sizing engine reads your sales rate, stock on hand, coverage days, lead time, safety days and what is already inbound. Cost and price are not inputs to it, so a wrong cost cannot quietly shrink a recommendation or talk you out of a product. Margin may colour a row in the interface, it never moves or hides one, and nothing is filtered off your purchasing list on profitability grounds. Loss leaders and bundle components are your call, not the software's.

Cost then appears beside the quantity, where you can watch it doing its work. The plan's total is recommended units times your registered purchase price, the landed figure is broken out per unit on the replenishment card, and a received delivery recomputes the weighted average and shows it to you before anything is written anywhere. Writing it back into Shopify's own cost per item field is a switch you turn on, covered on the page about that field going stale. What a product earns after ad spend is a separate question with its own page.

Our own number carries a gap and you should know where. Duty is not inside the unit landed cost yet. It lives as one percentage you set yourself and does not feed the calculation, so on duty-rated goods our figure is short in exactly the direction this post is about, and the app prints that shortfall on screen rather than hiding it. Packaging and payment fees are not modelled at all. Nothing here watches your bank balance either, so we will not stop you committing to a plan you cannot fund.

None of which is a reason to wait for software. Ten minutes with a shipment folder is the fix that matters most here, because the order quantity was never the part that was wrong. The approval standing on top of it was. The quantity method itself, deadlines included, is in the replenishment guide.

Common questions

Does the cost price affect my reorder quantity?

In Restocio it does not. The quantity is built from your sales rate, lead time, coverage days, stock on hand and what is already inbound, and no cost or price is an input to that calculation. Check any tool you use on this point, because a system that trims quantities on margin is making a buying decision for you.

If the quantity does not change, why does a wrong cost matter?

Because you approve orders in money, not in units. A plan priced on a cost that is 22 per cent low looks 22 per cent cheaper than it is, so it gets approved whole instead of staged, and the difference shows up at the bank weeks later. The error also leans towards imported products, so the wrong lines get cut when you do trim.

Should I fix the cost field before my next order or after?

Before, if the next order is large, because the cost decides what you approve rather than what you order. Start with the products carrying the most purchase value in the plan, since those are where a percentage error turns into real money. The rest can wait for their next delivery, which is the moment you have the invoices in front of you anyway.

Will Restocio stop me ordering more than I can afford?

No. It shows what the plan costs using the purchase prices it has, and it will not check that against your bank balance or hold a line back because money is tight. Cash-aware purchasing is on the roadmap under consideration rather than shipped, so treat the total as information for your decision, not a limit on it.

Marcus Volsted

Co-founder, Restocio

Marcus co-founded Restocio and works on it daily with a Swedish importer who plans their purchasing in it every working day. Restocio is built in Sweden by two founders, one Swedish and one Danish, and Marcus is the Danish one. Most of the examples on this blog come from that store's real ordering decisions rather than from a textbook. Why we are building it.