In the heat of house-hunting, it can be easy to keep all the numbers in your head. You debate back and forth over which properties to target and for how much and under what conditions. But as the Trulia blog notes, if you mostly just do this mental math without putting it down on paper it can be easy to talk yourself into less-advantageous deals when the numbers in your head collide with the emotions in your heart.

For instance, the rush of getting that “instant equity” from buying a house for less than it used to be worth — never mind that that price may have been artificially boosted by the bubble — can muddle the cold calculations based on your wages and salary.

The Trulia blog writes:

On the scent of a good deal, and in the heat of the hunt, even the most meticulous homebuyer can go up a few thousand in offer price to beat out other buyers. No problem, right? Well, but then when the inspector uncovers a few needed repairs, they make a mental guess as to what they’ll cost, and add that in – again, mentally. Then, when the lender requires a few extra thousand bucks than expected to close, that goes on top, but again, only mentally. And mental money tends to stretch a bit longer than real money does!

So make sure to bust out the paper, pencil and calculator, or your favorite trusty spreadsheet program and keep track of every single line item. The extra amount you’re bidding, every repair, every cost turned up during inspection, every fee. Are you bringing the donuts to the closing party? Put in a line item for Dunkin.

“Surprises are for birthday parties,” says the Trulia blog, “Not for real estate transactions…”

5 Strategies for Navigating the Summer Clearance Sale – on Real Estate! [Trulia] (Thanks to c-side!)

Want more consumer news? Visit our parent organization, Consumer Reports, for the latest on scams, recalls, and other consumer issues.