Price a change order by adding up every real cost the extra work creates (materials, labor hours, equipment, your time), then dividing that total by (1 minus your normal margin) so the change carries the same profit as the rest of the job. Get the number approved in writing before anyone lifts a tool, and attach it to the original contract so it can’t get argued away at final invoice.
The homeowner points at a wall and says, “While you’re in there, can you just move that outlet?” You say sure, because it’s five minutes and you’re a reasonable person. Then it’s the outlet, then a second coat, then “can we swap the fixture,” and by the time the job wraps you’ve done four hundred dollars of work you’ll never see a dime for. Nobody was a villain. The margin just quietly walked out the door one small favor at a time.
That’s scope creep, and it’s one of the most reliable ways for a profitable-looking job to close out flat or negative. The fix isn’t being difficult with clients. It’s having a fast, boring, repeatable way to turn “can you just” into a priced, approved change order before the work happens.
Why unbilled change orders quietly wreck your margin
A change order feels small in the moment, which is exactly why it’s dangerous. One $150 add doesn’t register. But the extra work still eats billable hours, still burns materials, and still pushes your finish date. If you’re running a 30-40% margin and you give away $1,200 of unbilled adds across a job, you didn’t lose $1,200 of profit. You lost the profit and you covered the cost out of your own pocket, so the real hit to your bottom line is bigger than the sticker.
The other trap: unbilled changes reset the client’s expectations. Once “can you just” gets a yes for free, every future request starts from free. You’ve trained the customer to treat your labor as a rounding error. Pricing the first small change politely and promptly is what protects the big ones later.
How to price a change order: cost first, then your normal margin
Two steps, and people usually get the first one roughly right and the second one wrong.
Step 1 — Add up the true added cost. Not just the obvious materials. Include:
- Materials for the change, at what you actually pay including tax and any small-order surcharge
- Labor hours (yours and your crew’s) at your loaded cost, not just wages
- Equipment, disposal, permits, or an extra trip if the change forces one
- The knock-on time: rework, re-sequencing, or the hour you lose because now you’re waiting on a part
Step 2 — Apply your margin the right way. This is where money leaks. Most people take the cost and multiply by their margin as if it were a markup. If your target is 35% and the added cost is $1,200, they quote $1,200 × 1.35 = $1,620. That feels right and it’s wrong. Multiplying cost by (1 + margin) gives you a markup, not a margin. To actually keep 35% of the sale price as profit, you divide:
Price = Added Cost ÷ (1 − your margin)
$1,200 ÷ (1 − 0.35) = $1,200 ÷ 0.65 = $1,846
That $226 gap between the markup math ($1,620) and the margin math ($1,846) is pure profit you’d have handed over by accident. The bigger your margin target, the wider that gap gets, which is why the shortcut quietly costs the most on exactly the work you most wanted to be profitable.
Watch out: “Markup” and “margin” are not the same number and treating them as interchangeable is the single most common change-order pricing mistake. A 50% markup is only a 33% margin. If you’ve been multiplying cost by your margin percentage this whole time, you’ve been undercharging on every add you’ve ever written.
Markup vs. margin: what you actually keep
Here’s the same $1,200 added cost priced both ways, so you can see how much the method itself is worth.
| Target margin | Wrong way (cost × margin) | Right way (cost ÷ (1−margin)) | Profit left on the table |
|---|---|---|---|
| 20% | $1,440 | $1,500 | $60 |
| 35% | $1,620 | $1,846 | $226 |
| 50% | $1,800 | $2,400 | $600 |
If you don’t want to run the arithmetic on a ladder or in a truck cab, a free change order cost calculator does the divide-by-(1−margin) math for you and spits out the price in a few seconds. Punch in the added cost and your margin, and you’ve got a defensible number before the client’s finished asking.
Get written approval before you do the work
A verbal “yeah, go ahead” is worth exactly nothing when the final invoice lands and the customer’s forgotten they ever asked. The single habit that separates contractors who collect on changes from the ones who eat them: approval in writing, before the extra work happens, every time, no exceptions for small stuff.
It doesn’t need a lawyer or a portal. A change order that holds up has four things on it:
- What’s changing — one or two plain sentences describing the added scope
- The price — the number, stated as an addition to the original contract
- Schedule impact — “adds one day,” even if that day is zero
- Approval — a signature, or at minimum a text/email reply that says “approved” with the dollar amount visible in the thread
A texted photo of a handwritten slip with a thumbs-up back counts. The point is a timestamped record that the customer agreed to the number before you spent the money. When you frame it as “quick heads up, that moves the price to X and adds about a day, good to proceed?” almost nobody balks. They balk when they see it for the first time on the final bill.
A worked example, start to finish
Say you’re mid-bathroom-remodel and the homeowner decides they want the shower niche tiled in a different, pricier mosaic than the contract called for, plus a second niche that wasn’t in the plan.
- Upgraded mosaic tile, net of the material you already priced: $180
- Second niche framing, waterproofing, extra tile: $140 in materials
- Added labor, 6 hours at your $55/hr loaded cost: $330
- Extra half-day of schedule and one supply run: baked into the labor and a $20 trip cost
Added cost totals $670. Your normal margin on this job is 35%. So the change order price is $670 ÷ 0.65 = $1,031, call it $1,030. You text the homeowner: “The upgraded mosaic plus the second niche runs $1,030 and adds about half a day. Want me to proceed?” They reply “yes go for it.” You screenshot that, note it on the change order line, and keep tiling. You just protected your 35% instead of doing $670 of work for a warm feeling. If you’d markup-mathed it at $670 × 1.35 you’d have quoted $905 and quietly given up $125 on one small change. Run that mistake across a dozen changes a year and it’s real money. Running these through a change order calculator keeps the margin math honest even when you’re pricing on the fly.
Frequently asked questions
What’s the difference between markup and margin on a change order?
Markup is a percentage added on top of your cost; margin is the percentage of the final price that’s profit. A 50% markup is only a 33% margin. To hit a target margin you divide cost by (1 − margin), not multiply by (1 + margin), or you’ll undercharge every time.
Should I charge my normal margin on change orders, or more?
At minimum, your normal margin so the added work is as profitable as the rest of the job. Many contractors add a few points on top because mid-job changes disrupt sequencing and pull you off plan. Charging less than your base margin means the change is dragging your whole job’s profitability down.
Do I really need written approval for small changes?
Yes, and small changes are where it matters most because they’re the ones people forget agreeing to. A quick text or email that shows the dollar amount and gets a “yes” back is enough. The rule is written approval before the work, no size exception, because “small” is exactly what gets disputed at final invoice.
What do I do when a client refuses to pay for a change they requested?
This is almost always a documentation problem, not a client problem. If you have a timestamped approval showing the price before the work, you have a clear position. Without it, you’re negotiating from nothing. Going forward, no approval means no work. It’s the cheapest insurance in the business.
How do I price a change order when I don’t know the exact cost yet?
Price it as a not-to-exceed number or a documented time-and-materials rate, and get that approved. Don’t do the work on a vague promise to “settle up later.” If it’s genuinely unknown, quote a cap the client approves, then bill actuals under it.
How should I track change orders so they show up in my books?
Log each one against the job with its cost, price, and approval, the moment it’s approved, not at month-end when you’ve forgotten half of them. That way each job’s true margin includes the changes, and you can see whether your change-order pricing is actually holding. Tabby captures this alongside the rest of your job’s income and expenses automatically.
Stop letting change orders erode your job margins.
Tabby is AI bookkeeping built for contractors and home-service pros. It tracks every job’s income, materials, and change orders so you can see real margin per job, not a guess at year-end. See how Tabby works or start a free trial and get your job numbers straight before the next “can you just.”
