Short answer: Home buying "rules" are quick guidelines, not laws. The 3-3-3 rule is about affordability (price around 3x income, 30% for housing, 30% saved). The 80-10-10 rule is a loan setup that avoids PMI. The 28/36 rule is how lenders traditionally measure debt. The 3-7-3 rule is about mortgage disclosure timing. Here's what each one means and how it applies to buying in Houston.

The 3-3-3 rule (also called 30/30/3)

This is a conservative affordability check with three parts:

• 30% for housing: Keep your total monthly housing payment (principal, interest, taxes and insurance) at or below 30% of your gross monthly income.
• 30% saved: Have about 30% of the home's price in savings, such as 20% for a down payment plus 10% for closing costs and reserves.
• 3x your income: Keep the purchase price around 3 times your annual household income.

Houston reality check: Few first-time buyers have 30% saved, and that's okay. FHA loans allow 3.5% down, and Texas has down payment assistance. Treat 3-3-3 as a "very comfortable" target, not a requirement.

The 80-10-10 rule (piggyback loan)

An 80-10-10 is a way to finance a home with 10% down while avoiding private mortgage insurance (PMI):

• 80% first mortgage
• 10% second loan, often a home equity loan or line of credit
• 10% down payment from you

It can make sense for buyers with strong credit who want to avoid PMI. The second loan usually has a higher, sometimes variable, rate, so compare it against a single loan with PMI.

The 28/36 rule

This is a classic lender guideline:

• 28%: Your housing payment shouldn't exceed 28% of gross monthly income.
• 36%: All your debts combined, including housing, shouldn't exceed 36%.

Today many loans allow more. FHA and many conventional loans often approve buyers up to about 43% total debt-to-income, sometimes higher. But 28/36 is still a good budget for living comfortably. Example: On $90,000 a year ($7,500 a month), 28% is a $2,100 housing payment and 36% is $2,700 for all debts.

The 3-7-3 rule

This one is about federal mortgage disclosure timing, not affordability:

• 3: Your lender must send your Loan Estimate within 3 business days after you apply.
• 7: The Loan Estimate must be delivered at least 7 business days before closing.
• 3: You must receive your Closing Disclosure at least 3 business days before closing.

These waiting periods protect you by giving you time to review your loan terms. Factor them into your closing timeline.

Other rules of thumb you'll hear

• The 1% rule for maintenance: Budget about 1% of the home's value each year for repairs.
• The 5-year rule: Buying usually makes more sense than renting if you plan to stay at least 5 years, because it takes time to cover buying and selling costs.
• The 20% down rule: Mostly a myth today. 20% avoids PMI, but most buyers put down less.

Which rule should you follow?

Use these rules as guardrails, then look at your real numbers. In Houston, property taxes and insurance make a big difference, so always look at the full monthly payment. See our breakdown of the monthly payment on a $250K home in Texas and how to get pre-approved in Houston.

Ready to look? Search homes for sale in Houston and surrounding cities.

This article is general information, not financial advice. Talk with a licensed lender about your situation.