How to Protect Your Housing Budget From Rising Mortgage Rates

The 30-year fixed mortgage rate hit 7.5% last week, another reminder of how quickly borrowing costs can move. 

If you're planning to buy a home sometime in the next year, that kind of move could change what you can afford by about $170,000.

I know rates have a lot of buyers in San Diego feeling stuck right now, wondering if they can even manage a payment if rates keep climbing. I get it.

And if moving is on your radar in the next three to twelve months, knowing how much cushion to build into your budget is essential. 

Realtor.com pulled over 20 years of mortgage rate data and built a framework I want to share with you. It breaks down how much room to build into your budget, whether you're buying in the next year, six months, or three months. 

How to Read the Numbers

Before we get into the numbers, a quick translation.

When you hear “basis points,” think of them as a simpler way to describe changes in interest rates. 100 basis points equals 1 percentage point, so a move from 7% to 8% is a 100-basis-point increase. A 50-basis-point move would be half a percentage point.

For the examples below, I’m using San Diego County’s $925,000 median home sale price, a 10% down payment, and a 7% interest rate as the starting point. That works out to an $832,500 loan with a monthly principal and interest payment of about $5,539.

From there, the question is pretty simple: if you wanted to keep that same monthly principal and interest budget, how much home could you afford if rates moved higher or lower?

That’s what the “buying power” numbers below are showing. And just to be clear, these examples are principal and interest only, so your actual monthly housing cost would also include things like property taxes, homeowners insurance, and possibly HOA dues.

Buying in the Next Year? Build In 100 Basis Points

Realtor.com looked at how mortgage rates moved over 12-month periods going back to 2000, comparing each month's rate to where it stood a year earlier.

Rates barely moved during most 12-month stretches. They stayed within 25 basis points up or down 29.1% of the time, the single most common outcome in over 20 years of data.

The middle 80% of outcomes ranged from -98 to +94 basis points. In plain English, that means that in 8 out of 10 historical 12-month periods, mortgage rates moved by roughly 1% or less in either direction. Round that up and you get an easy number to remember. If you're a year out from buying, build in 100 basis points of movement in either direction. 

Here's what that 100 basis point cushion looks like for a $5,539 monthly principal and interest budget:

• At a 6% rate, you could take on a loan balance of $923,799

• At an 8% rate, that drops to $754,826

• The swing between those two numbers comes to more than $169,000 in buying power

Buying in the Next Six Months? Build In 75 Basis Points

Cut that window down to six months and the range gets tighter. The middle 80% of six-month rate changes ran from -63 to +63 basis points, so the cushion rounds down to 75 basis points. Put another way, as you get closer to buying, the range of likely rate movement historically gets smaller.

Rates stayed within 25 basis points 37.2% of the time here, a bit more predictable than the 12-month window.

For that same $5,539 monthly budget:

• At 6.25%, you could take on a loan balance of $899,543

• At 7.75%, that falls to $773,108

• The difference between the two comes to more than $126,000 in buying power

Closing in the Next Three Months? Build In 50 Basis Points

Get within three months of closing and the range narrows even more. The middle 80% of three-month rate changes ran from -40 to +45 basis points, rounding to a 50 basis point cushion. That's why someone planning to close in the next few months generally doesn't need to build in as much room for rate movement as someone who's still a year away.

Rates moved less than 25 basis points in either direction 49.7% of the time on this window, close to a coin flip in favor of things staying stable.

For that same $5,539 monthly budget:

• At 6.5%, you could take on a loan balance of $876,273

• At 7.5%, that drops to $792,124

• The difference between the two comes to about $84,00

Here's what that looks like against the median priced home in San Diego, $925,000 as of August, with a 10% down payment. At a 7% rate, the monthly principal and interest payment comes to $5,539.

See how that payment moves in both directions:

• At 6.5%, it drops to $5,262, about $277 less per month

• At 7.5%, it climbs to $5,821, about $282 more per month

What You Can Do Right Now to Protect Your Budget

Whichever window you're in, here are a few things I'd encourage you to do before you start touring homes.

• Run your numbers at more than one rate scenario 

• Ask about your fallback options if rates move higher, like a rate buydown, seller concessions, or adjusting your down payment or target price

• Pay down revolving debt where you can. It helps your debt-to-income ratio and gives you more room to work with

Plan Now So You're Ready When You Find the Right Home

Building in enough room here means a rate move won't knock you out of your search.

If you're thinking about buying in San Diego in the next year, six months, or three months, let's sit down and run your numbers together before you start looking at homes. 

I'd rather help you plan for this now than have you find a home you love and hit a wall at the finish line.