A co-signer on a lease is a person who signs the lease along with the tenant to assure financial responsibility to the landlord. They have a good credit score and a high income. A co-signer is equally responsible for splitting rent, utility fees, and making timely monthly payments. They function as a safety net for the landlord in case the tenant fails to pay rent or breaches the leasing agreement. A co-signer can live in the apartment and has more rights, unlike a guarantor. However, they also take on the same financial responsibility as a tenant and then some. This means that if the tenant fails to pay rent, the co-signer is equally responsible for covering the rental payments. It is important to note that when a co-signer signs the lease, they sign for the whole lease, not just the portion that applies to the person they are co-signing for. Therefore, it is crucial for co-signers to be fully informed about what they are agreeing to and to ask any questions they have along the way.