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That guideline typically applies to consumer credit card account debt.  If you have no credit cards at all, your available credit would be $0.  This is not based upon income or your other types of debt like the auto loan.  If you have an account at Credit Karma (or any of the other similar free credit score sites), it should show you your total credit available.  Mint and Turbo seem to include all loan data, so if your auto loan was originally for $25,000 and you've since paid it down to $10,000 and this was the only reported debt on your credit report, then Mint and Turbo would probably show you at 40% utilization ($10,000 current balance divided by the $25,000 original loan amount which was the time when you had the most credit granted to you).  Depending upon your particular lender, that small lending loan may or may not show up on your credit report.