Many of us don't think about our credit score until it's time to make a major purchase or open a charge account. But that three-digit number affects a lot more than your credit. It can have a bearing on your auto insurance rates.

All those decisions you've made over the years to pay or not pay off credit card balances; transferring balances from one card to another; signing up for every credit card offer you get in the mail; and getting "upside-down" on your automobile loan where you actually wind up owing more than the vehicle is worth show up on your credit history.

After all, when we buy something from someone with a future promise to pay, we become a risk to that individual or institution.

Your credit score ranges from the low 100s to the 800s, the best possible score group. The higher your credit score, the lower risk you might be.

The big three credit reporting companies: Equifax, Experion and TransUnion keep your credit history and report to lenders or those from whom you make big purchases such as furniture, appliances and vehicles.

There are also specialty credit bureaus such as FICO and ChoicePoint that might have a great deal to do with what you can qualify for when purchasing a vehicle and/or what rate you pay when you obtain auto insurance.

Many auto insurers are actually composed of several companies that accept customers with differing qualifications as to their level of risk to the insurer.

If you have an excellent driving record and stable credit history, you might qualify for the company that offers the lowest rates. A driver who has good credit but has a spotty driving record might qualify for placement in another company that accepts higher risk drivers, which also means at higher premium levels.

A really good credit history can reduce your rate by half, but on the other side, negative credit issues can increase your base rate by as much as one and a half times. But age and marital status are also determining factors.

For example, a 31-year-old married male's base rate of $100 a month could go down by $20 with good credit, or an 18-year-old male with spotty credit could see a five-fold increase of $500.

Even where you live is a factor. Big city versus small town or rural area can have up to a $40 difference on a $100 base rate.

Obvious factors, the vehicle to be insured and your driving record, will further affect your rates.

Your vehicle can decrease or increase your insurance rate depending on whether you drive a "family car" or a "muscle car." On a $100 base rate, it could lower to $80 or increase to $150.

Points on your driver's license (speeding tickets and other bad driving habits) can increase your base rate from 1.75 to 2. In short, your base rate could double.

On top of these issues that directly affect your liability and physical damage rates, you might qualify for discounts that can be helpful, such as driver's training classes. However, your largest benefits come from a reasonable vehicle, a spotless driving record and a good credit record.

David Colmans is executive director of Georgia Insurance Information Service. Contact him at 770-565-3806 or by e-mail at dcolmans@giis.org.