Been looking at mortgage interest rates lately and noticed something interesting about where things stand. Back in September 2024, the average rate on a 30-year fixed was hovering around 6.69% with 15-year rates at 5.74%. If you're thinking about locking in mortgage interest rates, it's worth understanding what actually moves these numbers.

Turns out there are basically two categories of factors. Some you can't really control - the Fed's decisions on rates, what's happening with Treasury bonds, inflation levels, and overall economic health all play a role. When the economy is strong and inflation picks up, lenders tend to raise mortgage interest rates to compensate. On the flip side, when things slow down, rates usually come down too.

But here's what's useful to know: there are things you can actually influence. Your credit score matters a lot - anything 670 and above puts you in a better position. Lenders also look at your debt-to-income ratio (ideally under 43%) and how much you're putting down. That 20% down payment thing isn't just a number - it actually helps you skip private mortgage insurance, which saves real money. The loan term itself matters too. A 15-year mortgage will have a lower rate than a 30-year, but obviously your monthly payment is higher.

What's interesting is how different loan types work. Conventional loans from private lenders need solid credit and that 20% down. But if you're tight on cash, FHA loans only need 3.5% down. VA loans are even better if you qualify - no down payment required in most cases. USDA loans in rural areas don't need anything down either.

The whole APR thing is worth paying attention to - it's not just the interest rate, it includes lender fees too, so you get the real picture of what the loan actually costs. When you're comparing mortgage interest rates september 2024 levels or any time period really, that APR number tells you more than just the headline rate. On a $100,000 loan at 6.69%, you're looking at around $644 monthly, but over 30 years that adds up to over $130k in interest. That's why shopping around and trying to get your rate down even by a fraction of a percent actually makes a difference.