A guarantor, also called a co-signer, is a third party who signs your lease and legally promises to pay the rent and cover damages if the tenant does not. The guarantor does not live in the unit and has no right to occupy it, but their signature puts their own income and assets on the hook for the lease.
In practice
Say a recent graduate applies for a unit at $1,500 a month. Their credit file is thin and their job started three weeks ago, so they fall short of your income rule, which is usually monthly rent times three, or $4,500 a month here. You ask for a guarantor, and the applicant's mother signs. She earns $9,000 a month and has years of clean credit. You now have two signatures on the obligation.
Three months in, the tenant stops paying and owes $1,500 for the month plus a $75 late fee. Because the lease was signed jointly, you can pursue the tenant, the guarantor, or both for the full $1,575. If the tenant skips and leaves $900 in damage beyond the deposit, that figure is recoverable from the guarantor too. Guarantors are typically liable for the entire lease term, including a renewal in many states, so screen them as carefully as you screen the resident.
Why it matters to a small landlord
A guarantor is the tool that lets you say yes to a marginal applicant without eating the risk yourself. It is most useful for students, new earners, and people relocating before a job starts, the same files that fail a strict income or credit screen. Run the guarantor through your full process anyway: a guarantor with worse credit than the tenant adds paperwork and no protection. See tenant screening for the criteria to apply to both names, and make sure the guarantee is captured in writing as a lease addendum that names the lease, the term, and the exact scope of what the guarantor owes.
The reason a guarantor has teeth is joint and several liability: you can collect the whole balance from whichever signer can actually pay, rather than splitting it. Keep that paper close to your rent ledger so the amount owed is never in question, and remember a guarantor sits one step removed from a regular sublease, where a new occupant takes over the unit but your original tenant usually stays on the hook. A signature is only worth as much as the income standing behind it.