A co-signer is someone who agrees to share responsibility for a loan with the main borrower. Remember, if the borrower fails to make payments, the co-signer is legally obligated to pay back the loan. Co-signers are often used when a borrower has a low credit score or limited credit history, as adding a co-signer can increase the chances of loan approval. Having a co-signer helps reduce the lender’s risk, as there is another person who can step in if needed.