Lenders pay strict attention to your credit score and history when you apply for an unsecured loan. That's because with no collateral, all they have to rely on is your promise to repay your loan. Your past payment history tells them how likely you are to keep that promise. If you have a poor payment history and no collateral to pledge as security, adding a co-signer can convince a lender to take a chance on you. Of course, your co-signer is taking a big chance on you because co-signers get stuck for the loan if the primary borrower doesn't pay. And if you make late payments and the lender reports to credit bureaus, it can hurt your co-signer's credit score. So only add a co-signer if you are certain that you'll make your payments on time.