Most people who agree to guarantee someone’s lease have read the explanation of “guarantor vs. cosigner” a dozen times. What they haven’t seen is their own number — the actual dollar figure they’re agreeing to if things go wrong. That’s the gap this calculator fills: not another explainer, but the math itself, run on your specific rent, your specific lease length, and your specific deposit.

The formula, in plain terms

Worst-case exposure = (monthly rent × months remaining) + likely late fees + typical eviction/legal costs + estimated property damage − the security deposit already on file. Every term in that formula is something the articles already agree on individually — nobody had simply added them up into a single number you can plug your own lease into.

The trap that catches people off guard

Most people read “12-month lease” and mentally cap their risk at 12 months of rent. Two things commonly blow past that ceiling: a lease or guarantee that auto-renews without requiring your active signature again, and legal/reletting costs that get tacked onto the unpaid rent once an eviction actually starts. Neither is hidden exactly — they’re just buried in paragraph eleven of a document most guarantors never finish reading. The liability itself generally runs for whatever length of term is named in the guarantee — it’s the auto-renewal clause specifically that erases that ceiling, since a guarantee with no explicit end date can keep extending alongside the lease indefinitely.

Guarantor or cosigner — does it change the math?

Not the ceiling. A cosigner is treated as a tenant and can typically be pursued immediately, often folded into the same eviction case as the original tenant. A guarantor is usually contacted only after the landlord has exhausted collection efforts against the tenant, through a separate and slower civil action. The eventual dollar amount tends to land in the same place either way — the difference is mostly about timing and which legal door it comes through.

Two practical questions tend to follow the dollar figure once it’s real. Whether it touches your credit depends mostly on whether the account ends up reported to a credit bureau or pushed into collections or a judgment — simply being named as guarantor with no missed payments doesn’t, by itself, put anything on a credit report. And the agreement isn’t necessarily permanent: many landlords will agree to a written release after a stretch of consistent on-time payments from the tenant, though this has to be actively negotiated and put in writing — it’s never automatic just because time has passed.