How is a buyout price set?

Appraisal or market analysis

An appraisal is a formal valuation by a licensed appraiser, who is a different professional from a real estate broker. A comparative market analysis is a broker's opinion of likely sale price, built from recent sales and current listings nearby. Both look at comparable homes. They're written for different purposes and by people with different licenses.

If you're refinancing to buy your spouse out, ask the lender what valuation it will require. It may not be the one you two chose.

Neither one is right in every case, and which you use depends on what your attorneys, your lender or your written agreement calls for, and on how much you're willing to spend to settle the question.

Agree on the method before the number

This is the step that prevents most arguments. Once a figure is on the table, the person keeping the house tends to want it low and the person leaving tends to want it high, and every later choice looks like a move in that fight. Deciding the method first takes the number out of anyone's hands.

Write down who orders the valuation, who pays for it, which date it's measured on, and what happens if one of you rejects it, such as a second opinion with the two results averaged. Your attorneys can put that language into your agreement. The guide on pricing so nobody feels cheated walks through it.

Agree first. Then look.

Where I fit

I can prepare a CMA for the house and send the same copy, with the same comparable sales, to both of you at the same time. I won't adjust it for one of you or talk it over privately with either side. If you need a formal appraisal, I'm the wrong person; hire a licensed appraiser.

Short answer: pick the method together. Then the price follows. For what comes after, see can I keep the house and buy out my spouse?

If you've already disagreed

Sometimes this question comes up after the argument has started, with each of you holding a number from a different website. That's fixable. Set both numbers aside and agree on the method as if neither had been mentioned, with a written promise that you'll each accept the result or follow the dispute step you've chosen. Your attorneys or a mediator can help word that promise so it holds.