+1 to mortgage length. We heavily pivoted our decision to buy on getting a 7 year ARM because my friend and I knew we wouldn't grow old together there (wanting to do things like get married and have our own families). A time bomb on the mortgage was a feature, for us, and a cost savings.
It's a very poor rule of thumb. Contrary to the other comment, these costs don't increase linearly with value of the house. Sure, if I live in an expensive area, it may go up 30%, but not much more. Looking at how much my house has appreciated, I can assure you I pay not much more in maintenance than when I bought it.
The 1% rule came about when the median house price was under $200K.
Watch any one of the threads on "should I buy/can I afford/pros/cons", and you'll see a vocal subset who seem hellbent on convincing people that owning a house is nothing more than opening your wallet/checkbook/credit card every other weekend for the "next four digit maintenance issue".
(I feel the same way about having kids.)
Off the top of my head, some things I'd add to make this more useful to a wide audience:
- I don't know what I pay in state income and sales taxes. But I do know my income and my state's tax rate; income tax could be derived from that. I'm not sure how you'd estimate sales tax, though - you'd have to know how much of my spending is taxable.
- I've heard a rule of thumb that home maintenance costs are 1% of the home's value per year; maybe default to that, especially since a first-time home owner doesn't really know what those costs are. However, older houses will require more maintenance and that cost probably scales with square footage, not cost.
- you're assuming a 30-year mortgage - I'd put in the ability to change mortgage length. (Also, maybe a link to somewhere where I can find out what mortgage rates are.)