Several key mortgage rates inched up today. The biggest news was the meteoric rise in borrowing costs for fixed-rate 30-year mortgages, but it’s also worth noting that 15-year fixed rates surprisingly moved in the opposite direction. On the variable-mortgage side, the average rate on 5/1 ARMs also notched higher.

Rates for mortgages are in a constant state of flux, but they have remained in a historically low range for quite some time. If you’re in the market for a mortgage, it may make sense to go ahead and lock if you see a rate you like. Just make sure you’ve looked around for the best rate first.

30-year fixed mortgages

The average 30-year fixed-mortgage rate is 3.88 percent, up 41 basis points over the last week. A month ago, the average rate on a 30-year fixed mortgage was lower, at 3.34 percent.

At the current average rate, you’ll pay $470.52 per month in principal and interest for every $100,000 you borrow. That’s an additional $23.15 per $100,000 compared to last week.

15-year fixed mortgages

The average 15-year fixed mortgage rate is 3.07 percent, up 33 basis points since the same time last week.

Monthly payments on a 15-year fixed mortgage at that rate will cost around $694 per $100,000 borrowed. That may squeeze your monthly budget than a 30-year mortgage would, but it comes with some big advantages: You’ll come out several thousand dollars ahead over the life of the loan in total interest paid and build equity much more quickly.

5/1 adjustable-rate mortgages

The average rate on a 5/1 ARM is 3.27 percent, ticking up 26 basis points over the last seven days.

These types of loans are best for those who expect to sell or refinance before the first or second adjustment. Rates could be substantially higher when the loan first adjusts, and thereafter.

Monthly payments on a 5/1 ARM at 3.27 percent would cost about $436 for each $100,000 borrowed over the initial five years, but could increase by hundreds of dollars afterward, depending on the loan’s terms.