Fixed Price vs. Cost Plus: How to Compare Two Builder Bids

Two builders quote your project and one number comes in lower. That’s where most people start, and it’s a fair place to start.

But there’s a question sitting underneath both numbers that matters more, and it’s easy to walk right past: which of these is a number somebody can actually be held to, and what are the next 12 months going to feel like for you?

That’s really the fixed price versus cost plus question. It isn’t an accounting preference. It decides who absorbs it when the build costs more than anyone planned, and it decides how you’re going to spend your time while your house goes up.

The short answer

Cost plus means you pay the actual cost of the work plus the builder’s fee. The number you start with is an estimate, every overage is yours, and you’ll be reviewing invoices for the length of the build. Fixed price means the builder commits to a number up front and absorbs the difference if the work costs more, which only holds if real pricing work happened before you signed. We build fixed price. Here’s how each one works, and how to compare two bids fairly whichever way you go.

How does cost plus work?

You pay the actual cost of the work plus the builder’s fee, either a percentage of cost or a flat amount.

The mechanics are straightforward, and so are the tradeoffs:

• The number you start with is an estimate. Nothing in the structure obligates it to be right, and it isn’t what you’re agreeing to pay.
• Every overage is yours. Rock in the excavation, a framing crew that takes three extra weeks, lumber that moves between bid and buy. All of it lands on your side.
• If the build comes in under, you keep the difference. If that were to ever happen, that would be an upside.
• With a percentage fee, the builder’s pay goes up as your cost does. That’s an awkward thing to have sitting in a relationship, even when everybody involved is honest.

Seeing every receipt isn’t the same as knowing what you paid

This is the part that tends to get oversold. Cost plus often gets described as the open book option, as though a stack of receipts settles the question of what something should have cost.

It doesn’t. A receipt tells you what a line item cost the builder. It doesn’t tell you whether that was the best price available, whether the scope on a sub’s invoice matches what actually got installed, or what arrangement sits behind the number. A markup or kick-back can be built into a sub’s pricing long before an invoice is ever written, and when that happens the paperwork looks perfectly clean.

Most builders running cost plus aren’t doing that, and the model earns its place on work nobody can define up front, like a remodel where the wall could hide anything. But receipts can’t tell you which kind of builder you’ve got, and on a house that can be defined in advance, that’s a lot to leave to paperwork.

The point is this: the receipt isn’t the protection people assume it is, and a fixed price isn’t hiding something by not producing one. They’re two different promises. One says here’s what we spent. The other says here’s what you’ll pay, and we’re the ones on the hook if we got it wrong.

Why we build fixed price

The builder commits to a number. If delivering the agreed scope costs more than that, the builder absorbs the difference.

That does three things for you:

• You can plan. Your lender can underwrite it, and you know what you’re committing to before you commit.
• The overage risk sits with the person who can influence it. We’re the ones picking the subs, running the schedule, and buying the material. We should carry the consequences of getting that wrong.
• You stay in the part of this that deserves your attention. Selections, the layout, how the house actually works for your family.

That’s our call, not a verdict on anybody else. Plenty of good builders run cost plus well. We chose fixed price contracts because we’ve seen what an open ended number does to a family halfway through a build, when the total keeps climbing and there’s nothing left to do but keep writing checks. We decided we never want to put a family in that position.

Fixed price does have a real weakness, and you should know it going in: it’s only as good as the homework behind it. A number put together in an afternoon isn’t fixed, it’s a guess with a signature on it, and guesses get corrected later through change orders. So the fair question to ask anyone quoting you a firm price is what that price is built on.

What makes a fixed price actually hold?

Here’s what’s underneath ours, so you’ve got something concrete to hold other numbers up against.

We price from finished plans rather than sketches. We use real trade partner pricing on your actual scope instead of last year’s square foot average. Allowances get set at what the thing you want actually costs at a named local supplier. Site work gets priced after we’ve walked your lot, because that’s the line item that moves the most. Then it goes in writing before ground breaks.

That takes weeks, which is why it happens inside a pre-construction agreement instead of for free in a few days. If a builder hands you a firm number in 48 hours, just ask what it’s based on. Sometimes the answer is good, like they’ve built that exact plan four times already. Often it’s a square foot average, and averages get corrected later at your expense.

How do you compare two bids fairly?

Whichever model you land on, price is the last thing to compare, not the first. Work through these before you look at the totals.

Is the same scope inside both?

Site work. Utilities. The driveway. Permits, engineering, geotechnical reports. Landscaping. Appliances. Window coverings. Any one of those left out makes a bid look sharper, and it turns into something you have to buy anyway later on.

Ours includes permits, engineering, and geotechnical work. Not everybody’s does, and that isn’t a knock on them, it’s just a different way of presenting the same project. Ask both builders where theirs sits.

What are the allowances set at in real dollars?

This is where a low bid hides most comfortably. An allowance is money set aside for something you haven’t picked yet: flooring, lighting, plumbing fixtures, countertops. Set them low and the total looks great.

Then you get to the showroom, and nothing inside the allowance is anything you’d actually put in your home. The difference comes back as a change order, after you’re committed.

So ask for each major allowance in dollars, then ask what that buys at a named local supplier. A builder who’s done the work can show you. A builder who hasn’t will talk about quality in general terms.

What square footage is the per foot number measured against?

A per foot figure is a total divided by an area, so it moves when either one does. Quote it against living space only, leaving out the garage, the covered patio, and the deck, and the rate looks excellent while the home you’re building is considerably bigger than the number describes.

Ask which area each builder used. If the two of them are measuring differently, the rates simply aren’t comparable, and neither one is wrong.

What happens when the price moves?

Under what circumstances can the number change? What’s the change order process, and who signs? Is there a contingency, who holds it, and what happens to whatever’s left at the end?

A contract that can’t answer those has postponed the argument, not prevented it.

What’s the payment schedule tied to?

Payments should track completed work that somebody has verified, not a calendar. If the schedule is running out ahead of the progress, it’s fair to ask why.

The comparison in one table

Ask both builders	What a weak answer sounds like
What’s excluded from this number?	“Everything you need is in there”
What are the allowances, in dollars?	“We use quality finishes”
Which square footage is the rate measured against?	“Standard square footage”
When can the price change?	“Only if you change something”
Fixed or cost plus, and who eats the overage?	“It works out about the same”

None of those weak answers means somebody’s being shady. Often it just means the work hasn’t been done yet. Either way, you want it done before you sign.

The bottom line

Cost plus moves the cost risk onto you and puts a stack of invoices on your kitchen table every month. Fixed price moves that risk to the builder, but it’s only worth something if the builder did enough work up front to know the number is real.

So when you compare two bids, you’re not really comparing prices. You’re comparing what each builder is willing to be held to, and what your next year is going to look like. A number that comes with a defined scope, allowances in dollars, and a clear process for what happens when something moves is worth more than a lower number with none of that behind it.

If you’ve got a bid in hand and want it read line by line, bring it to us. That’s a budget review, and we’ll tell you plainly what we think of it, whether or not you build with us.