*Loan,banking and credit>>>auto loan

If I get a co-signer for my auto loan, will I get a better interest rate?

I'm about 680 and they are giving me 11%. My co-signer is way better, so I was hoping that if she was on my loan, I could get a much better interest rate. How do they calculate it?

Your credit score is not the only thing that lenders use to determine your interest rate:
If you do not have previous auto loans, you might get a higher rate
If you have a short job history, ditto
If you're putting little- no down payment, ditto
If you are applying for an extended term loan, ditto
If you're trying to finance an older vehicle, ditto
etc

If you use a co-signer, you will also be 'tying up' their credit & then they may not be able to get a loan for themselves.

A 680 score is not bad but it's also not stellar, that might be because you haven't been in the 'system' all that long or you may have alot of debt, or you might be applying for too much credit.
If you want a lower interest rate, try talking to a few different lenders and/or make some adjustments in: the term (shorter), money down (more), vehicle (newer or less expensive) Source(s): In the auto bussiness since 1983

Not neccessarily. Some banks give loans based on the weaker individual's credit score. 680 isn't bad, maybe you should shop for a rate.
Used to work for a car dealer.
You can do better than 11%. Try this http://painintheexhaust.blogspot.com... You don't need a cosigner to get a better rate just shop around more.
Depending on what your credit actually looks like, you should be able to get a better rate. Try a credit union.