Cell site rent generally increases on a periodic basis (either at each renewal term or annually). Usually it’s a fixed percentage — between 1 and 3 percent per year, but sometimes it’s indexed off a national or local key economic indicator, with the most common index being the consumer price index (CPI).
I ran across a podcast on NPR’s Planet Money where they followed around one of the surveyors who gathers data to calculate CPI, and the podcast provides an interesting introduction of what goes into calculating it. The CPI is made up the price of thousands of items, and a federal agency has the task of visiting stores around the country, looking up the price of key items and determining if the prices described by the CPI are going up or going down. Is the price of a size 14 boy’s shirt the same as it was last month or has it increased? How about the price of bacon? All these items are considered. As you can see from this example table (out of a 100 page document), scores of factors are tracked and considered to calculate CPI.
This affects cell site rents because the CPI is impossible to predict. If a wireless operator has to predict their budget over the next three years and they have cell site rent escalators that are tied to CPI, they have no way of knowing exactly what they owe or what their rent expense will be. As a result, wireless operators have moved away from signing new leases that have variable escalation terms. Instead, whenever possible, they enter into long term leases with fixed escalation terms over the life of the lease. In addition, operators are pursuing initiatives to lower their lease expense through eliminating CPI escalation terms in existing cell site leases through negotiations with landlords.
CPI has averaged approximately 3% over the last ten years. This is a historically low value that has coincided with very low interest rates among other factors. The fact that CPI has remained a low value for a relatively long, ten year period, allows operators to substitute a fixed percent escalator at an attractive long term rate.