Knowledge about interest rates, like most kinds of information, is most useful when it's seen in perspective.

That is, if you're looking to get a mortgage or auto loan, it's very important to know what the appropriate rate is today. But it's also important to know what it was last week and last month so you can get a better idea of which way it's moving. An interest rate that looks good to you today might not look so good if you have reason to believe it will be even lower next week.

Key interest rates Jan. 1, 2001 - Sept. 17, 2007 Note: In late 2006, Bankrate changed which credit cards were included in this chart. It now uses an average of all fixed-rate cards.

Bankrate has taken a good look at which way interest rates have been moving in five important categories -- mortgages, home equity lending, certificates of deposit, auto loans and credit cards -- and how much they've moved.

Studying the recent history of interest rates might help you make a better decision on what to do next.

Mortgages
ARMs: Since mid-August, ARM rates had mostly been falling as investors became convinced that a Federal Reserve rate cut was forthcoming. On Aug. 22, Bankrate's benchmark rate on the 5/1 ARM reached 6.64 percent, the highest it had been in two months.

Then it fell, landing at 6.3 percent three weeks later. It's likely to stay around there or maybe fall even farther. The benchmark one-year ARM had been rising most of the summer before finally falling slightly last week.

Fixed: Fixed-rate mortgages have yo-yoed all year. They have fallen more than half a percentage point since July on expectations of a Fed rate cut.

See mortgage rates in your area.

Home equity borrowing
HELOC: Rates on home equity lines of credit move up and down with the prime rate, which, in turn, moves up and down with the target federal funds rate. Now that the Federal Reserve has cut the federal funds rate by a half point, rates on HELOCs will fall a half point.

Home equity loan: Home equity loans have been pretty steady all year. They're about 11 basis points higher than at the beginning of the year, even as the federal funds rate has remained unchanged. A half-point Fed rate cut doesn't translate automatically into lower rates on home equity loans, but it makes them likely.

See home equity rates in your area.

Certificates of deposit
CD yields have bounced around a little bit, but for the most part they've held their ground so far this year. The average three-month yield, as surveyed by Bankrate.com, was 2.90 percent Jan. 3 and today stands at 2.91 percent. To date, its monthly average hasn't been higher than 2.94 percent or lower than 2.88 percent. The story is similar for the six-month, which began the year at 3.54 percent and is now at 3.53 percent; the one-year ranging 3.78 percent to 3.75 percent; and the five-year 4.07 percent to 4 percent.

See CD rates in your area.

Auto loans
This year auto loans have kept a pretty steady course, varying by an average of about a third of a percent as the year has progressed, according to weekly Bankrate.com interest rate surveys.

In mid-January rates lurched upward to hit the high for 2007; 7.95 percent for the standard 60-month new car loan and, in the same week, 8.8 percent for the 36-month used car loan rate. The five-year rate dipped to 7.7 percent at the beginning of May and floated there for six weeks, along with the three-year loan rate at 8.46 percent.

See auto loan rates in your area.

Credit cards
The federal funds rate is now 4.75 percent after the Fed cut the rate by a half-point.

Interest rates on all cards -- standard, gold and platinum -- both fixed and variable, have remained relatively flat for nearly a year. Expect them to decline. Currently, the standard fixed-rate is 13.48 percent and the standard-variable rate is 14.57 percent.