Ask an operator what a rollover costs and most will quote the downtime: six months of missing rent, say. That answer is not wrong. It is just the smallest number in the stack, and pricing a rollover at the smallest number in the stack is how deals get bought on assumptions that were never really examined.
Stack the full cost of one tenant leaving. Start with the lost base rent across the downtime, the part everyone counts. Add the lost expense recoveries: on a triple net lease, an empty suite is not just earning nothing, it has converted its share of taxes, insurance, and CAM from the tenant's problem into yours, every month it sits dark. Add the tenant improvement package it takes to sign the replacement, which in many markets has grown faster than rents have. Add the leasing commission on the new lease. Add the free rent months it took to win the tenant, which are invisible in face rent and very visible in cash flow.
By the time the stack is complete, a rollover that reads as six months of rent frequently prices out at twelve to twenty months of rent in true economic cost. That ratio is the point of this page. The widget below lets you run it on your own numbers.
Now the part the napkin math cannot do, which is why this page ends where a simulator begins. First, rollovers are probabilistic. A tenant with a seventy percent renewal likelihood does not either cost you nothing or cost you the full stack. Priced correctly, that lease carries a probability-weighted rollover cost every time you underwrite it, and a rent roll with five expirations in the hold carries five of them. Second, rollovers cluster. Two leases expiring the same year do not just double the cost, they can drag occupancy through a debt covenant or land in the exact year your refinance was planned. Third, the cost lands somewhere in time. A rollover in year two hits your capital plan; the same rollover in year nine hits your exit NOI and therefore your sale price at whatever multiple the market is paying.
A spreadsheet with a blanket vacancy factor sees none of this. It smears a percentage across every year and calls the risk handled. The whole discipline of rollover underwriting is refusing that smear: this tenant, this expiration, this probability, this downtime, this package, and then letting the model show you what the schedule of expirations does to the deal as a whole.
PropCalc™ models rollover at that level natively, per tenant, with the downstream math wired through the pro forma, the debt, and the exit. The widget below is deliberately simpler than that. It prices one rollover, fully stacked, so the next time someone quotes you six months of rent, you know what number to actually write down.