How do you calculate a mortgage in your head?

[Nick Brimmerq]

Hello!

I am curious how you all seem to calculate a mortgage payment on the spot. This seems crucial when you are in the middle of a negotiation on purchase price, possibly trying to push the price lower or knowing when to walk when the price to CoCROI gets too high. 

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The equation I seem to think of is this

((<Purchase Price> * .01) / 2) + (<PurchasePrice> * .002)

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So an example of this would be:

($280,000 * .01) / 2 + ($280,000 * .002)

$2,800 / 2 = $1,400 + 280 = $1,680

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I seem to be within $5 of every mortgage I am considering. Yes, I know this does not include utilities or HOA or anything else.

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And yes, if you guess, I'm a software engineer at a tech company, so I love algorithms to calculate things. :) 

Thanks.

- Nick