Here are some rules we don't follow:
1.
Don't buy a home more than 2 or 3 times income.Leverage is valuable. Your credit is an asset. It can make you a lot of money. Not to mention that many housing markets are now at a minimum of 5x income for the average two income family.
What matters is not the purchase prices vs. income, but the out of pocket after tax cost each month. What also matters is neighbourhood and the higher the value the better where I live. A multi-family property is a much faster and safer way to wealth creation than a SFH if you are prepared to hold for ten years or so and you are prepared to be a landlord.
For those of you who are scared of a crash or interest rate hike my view is that you can mitigate risk with the rental income, longer term mortgages and buying the right place. Sweat equity can be used here too. I have not found anything that gives a better ROI.
Do a ten year forecast and you can see how it works or not for your situation. Make sure you factor in all expenses and risks, as well as taxation.
2.
Operational expenses are going to cost 50% of rents.This is nonsensical given the variation in house prices and rental incomes for a similar home in different markets. A house that rents for $3000 a month in LA might rent for $800 a month in Louisiana.
What really matters is the condition of the major components of the home at time of purchase and their expected lifespan and your expected timeframe to hold the property (ie. are you going to have to pay for replacement). In addition, buy in good neighbourhoods with very low vacancy rates.
If you really want to know what your costs are going to be you need to do a capital asset inventory with present condition and expected lifespan and add some contingency. The expected lifespan of housing components is here:
http://www.nahb.org/fileUpload_details.aspx?contentID=993593.
Banking on the 4% rule.
The 4% rule is eye-opening and miraculous but you first have to save enough to get to the amount you need and it is possible that it will not work for you if you have new dreams you did not include in your calculations. In addition, it is possible that when you need more money one year the market will be down. There is a lack of both speed and peace of mind in relying on this alone for me.
There is a discussion on this here:
http://forum.mrmoneymustache.com/welcome-to-the-forum/forget-the-4-swr-or-any-swr-it's-all-about-income/4.
If you’re not willing to pay cash for it, then it doesn’t make sense to buy it on credit.The test for us is whether it results in a cash flow positive result at an acceptable level of risk. Housing is one example of this. Another might be business financing.
Even if you buy with cash, a depreciating asset is going to cost you money. Cars can made to work on a cash flow positive basis if you have an inexpensive fuel-efficient car and you receive reimbursement for mileage for work. We have friends who rent out their second-hand still newish $10,000 travel trailer as accommodation in a tourist area for $800 per week for six weeks and they use it the rest of the time. It doesn't get towed by renters as it is set up at a local campsite for them.
If you are going to buy a depreciating asset consider whether you can make it cash flow positive. If you can't, try to buy it at its depreciated value with enough useful life left unless other factors make it worthwhile to buy new like health and enjoyment.