A quick mortgage prequalification tool from Sky Minor, Mortgage Broker.

This is the original "quick and painless" mortgage prequalification equation 

It assumes interest rates below 5% and does not account for other debt obligations like student loans and car payments. It also does not factor in mortgage insurance, property tax payments or homeowners insurance.

1. Most importantly, Have W2 or 1040 tax returns to verify your income, at least 6% of the property purchase price for a down payment and a credit score of at least 600 to squeak by on an FHA loan. 

2. Take your household's gross annual salary or taxed net income and divide it by 0.2 That's all you have to do! I told you this was quick. For an example, let's use a household earning an income of $85,000 per year.

$85,000/0.2=$425,000

This family will qualify for about $425,000 of mortgage.

This is only an estimation but it's a good tool to gauge if you are ready to buy a property.