How to build a self-storage pro forma

Start from the unit mix

Storage revenue is built unit type by unit type, not as a single average rate across the building. A facility rents small and large units, climate-controlled and non-climate, and each type carries its own asking rate, its own demand, and its own vacancy behavior.

Lay out the rentable square footage by unit size and climate type, then attach an asking rate to each line from what the competitive set inside the ring currently charges for that same unit type. This is where a model most often goes wrong, because a blended rate hides the fact that the mix being built or bought does not match the mix the market wants.

For an acquisition, put the in-place rate and the current market asking rate side by side for every unit type. The gap between them, positive or negative, is the honest statement of the upside.

Revenue lines

Gross potential rent is the sum of every unit at its asking rate as though fully occupied. Everything below it is a deduction or an addition that needs its own justification.

Expense lines

Storage carries a lower operating expense load than most property types, which makes each line more visible and each error more consequential in percentage terms.

Property tax deserves its own attention on an acquisition, because many jurisdictions reassess on sale. Carrying the seller's tax bill forward understates expenses from the first year and is one of the most common modeling errors in the asset class.

Payroll or third-party management fee, insurance, utilities, repairs and maintenance, marketing, software, credit card processing, and administrative costs make up the rest. Climate-controlled buildings carry meaningfully higher utility cost, and that belongs in the model rather than in a blended per-square-foot assumption.

Capital reserves sit below net operating income. Roofs, doors, and pavement are the recurring capital categories in storage, and a model without a reserve line overstates distributable cash.

Lease-up modeling for a development

A new facility earns nothing on day one and reaches stabilization gradually. The absorption curve is the most consequential assumption in a development pro forma and the one least amenable to a rule of thumb.

Source it from how quickly comparable square footage has been absorbed in the same ring, and from how short the ring actually is on existing square feet per capita. A genuinely undersupplied ring fills faster, which is the screening question reappearing inside the financial model.

Model the operating shortfall through stabilization as a funded line in the development budget, not as a footnote. Underfunding it is what turns a slow start into a financing problem.

Stress the curve against the development pipeline. If an approved project inside the ring delivers during your lease-up window, absorption slows and achievable rates soften at the same time, and both effects belong in the downside case.

Structuring the model so it can be audited

The difference between a model a committee trusts and one it argues with is usually layout rather than mathematics. Keep assumptions in one place, formulas in another, and never bury a hardcoded number inside a calculation.

Give every assumption a source cell next to it. For rate assumptions that means the trade area, the unit type, and the date the rate was collected. For expense assumptions it means the quote or the comparable statement it came from. A reviewer who can trace any number in two clicks stops questioning the model and starts questioning the deal, which is the conversation you want.

Model monthly through lease-up and stabilization, then annually afterward. Storage moves too quickly for an annual model to represent absorption honestly, and a monthly view is also what a construction lender will ask to see for the interest reserve.

Keep the unit-type detail visible rather than collapsing it into a summary tab. The mix is where a storage model most often diverges from reality, and hiding it removes the reviewer's ability to catch the divergence.

Testing the model

Run a downside case that reflects the risk specific to storage rather than a generic haircut. The realistic downside is competing supply arriving in the ring, expressed as slower absorption plus softer rates together.

Check the sensitivity of the outcome to the exit capitalization rate. If the return only works when the exit cap is lower than the entry cap, the model depends on market conditions rather than on the asset, and that dependence should be stated plainly.

Confirm that every assumption has a source you could show a reviewer. An assumption without a source is a preference, and preferences do not survive an investment committee.

Date the rate evidence. Storage asking rates move frequently, so a model built on a rate table assembled months earlier may already describe a market that no longer exists.