Why Growth Space Creates a Distinct Modeling Problem
Signing a lease for space you do not yet need is one of the most common and underanalyzed decisions in corporate real estate. The headline ask seems straightforward — take extra square footage now, pay rent on it, and fill it as the organization grows. In practice, the lease economics are far more complex than that framing suggests, because you are effectively purchasing an option on future occupancy and paying a carrying cost every month until that option converts to productive use.
The core tension is between two legitimate business interests. The real estate team wants to lock in favorable conditions before the market tightens or the floor plate gets leased to someone else. Finance wants to minimize dead rent — rent paid on space that generates no revenue, no headcount productivity, and no operational output. Neither side is wrong, and the methodology for modeling growth space exists precisely to quantify the trade-off so the decision can be made on evidence rather than instinct.
Understanding how to model rent for growth space you will not fill right away is not simply a matter of running a standard discounted cash flow. It requires layering in contingency assumptions, sublease probability, free rent negotiation outcomes, and build-out timing — each of which shifts the effective cost materially. Getting those layers right is what separates a defensible board recommendation from a number that falls apart under the first follow-up question.
The sections that follow walk through each component of that model in the order a practitioner would build it, from setting the absorption timeline to calculating the true lease net present value and presenting it to decision-makers.
Defining the Absorption Timeline Before You Touch a Spreadsheet
Every growth-space model begins with an absorption assumption, and that assumption carries more weight than almost any other input. Absorption, in this context, means the rate at which the organization will actually occupy the excess square footage — expressed as a headcount forecast, a square footage per person allocation, or both.
The most common mistake is to use the business plan's best-case hiring scenario as the absorption input. Business plans are aspirational. For modeling purposes, you need a base case, a downside case, and an upside case, each tied to a specific headcount trajectory. The gap between those cases is what determines how much risk the organization is carrying when it signs the lease.
A useful framework is to divide the lease term into phases. Phase one covers the period from lease commencement to first occupancy of the growth space — this is pure dead rent. Phase two covers partial occupancy, where some portion of the growth space is in use but the remainder is still empty. Phase three is full occupancy. The model should assign a probability-weighted month to each phase boundary, not a single optimistic date.
Once you have the phased timeline, you can calculate the expected rent cost per occupied seat at each stage. If the blended rent is $50 per square foot and you are occupying 60 percent of the space, the effective cost per occupied square foot is roughly $83 — a figure that belongs in the business case alongside the nominal rent, because it is the number the business actually experiences.
Mapping the Free Rent Negotiation to the Absorption Gap
Free rent is the most direct mechanism for bridging the cost of growth space, and negotiating it effectively requires that your absorption model exist before the letter of intent is written. Landlords will grant free rent in exchange for lease term, credit quality, and market conditions. The question is how to size the ask so it covers the realistic absorption gap rather than a round number that feels good but does not actually match the exposure.
Start by calculating the expected months of dead rent under your base-case absorption timeline. If the growth space is 30 percent of the total leased area and the base case projects 18 months before that block begins to fill, the dead rent period on that portion is 18 months. That is your anchor for the free rent negotiation — you want to recover, at a minimum, a meaningful share of the carrying cost during that period.
Landlords will often prefer to grant free rent on the entire premises for a shorter period rather than a partial abatement on the growth portion for a longer one. Both structures can be modeled to an equivalent present value, and the choice depends on cash flow timing preferences. A shorter full abatement front-loads the benefit and is worth more in present value terms; a longer partial abatement spreads relief across the period when you actually need it.
When you receive competing proposals, translate each free rent structure into a monthly cash flow line and discount it at your organization's weighted average cost of capital. Comparing free rent structures on a nominal basis — "this one gives us six months, that one gives us eight months" — ignores the timing difference entirely and can lead to choosing the wrong structure.
Building the Sublease Assumption Into the Base Model
A sublease assumption should appear in every growth-space model, even if the organization has no current intention to sublease. Including it is not pessimism — it is an honest representation of the option value embedded in the space. If absorption falls short of projections, subleasing the growth space is the most common recovery mechanism, and the model should capture what that recovery would actually be worth.
The sublease assumption requires four inputs: the sublease commencement date, the sublease term, the sublease rent, and the sublease transaction costs. Each of these is uncertain, and each should be modeled in a range rather than a single point. Sublease commencement is typically six to twelve months after the organization decides to sublease — time to find a subtenant, negotiate, and document the transaction. That lag is a cost.
Sublease rent in a softening market will be below the master lease rent. In a tightening market it may exceed it, but conservative modeling assumes a discount. A hypothetical example: if the master lease rent is $55 per square foot and the sublease market supports $45, the carry loss on the growth space during the sublease marketing period — combined with the ongoing shortfall between master and sublease rent — should be expressed as a net present value figure in the model. Labeling it hypothetical is appropriate; inventing a specific market as the source of that figure is not.
The sublease transaction costs — broker commissions, tenant improvement allowances to the subtenant, and legal fees — reduce the net recovery meaningfully. Broker commissions on sublease transactions are commonly structured as a percentage of total sublease consideration, and subtenant improvement allowances can run several months of rent. The model should net these costs against the sublease income before presenting a recovery figure.
Calculating Effective Rent Across the Full Lease Term
Effective rent is the metric that consolidates all of the above into a single comparable figure. It expresses the average annual cost of the space, net of landlord concessions, spread across the full lease term. For growth space, calculating effective rent without adjusting for the absorption timeline produces a misleading number — one that understates the true cost in the early years and overstates the long-term efficiency once the space is fully occupied.
The correct approach is to calculate effective rent in two layers. The first layer is the standard effective rent calculation: take the total rent obligation over the lease term, subtract the value of free rent and any tenant improvement allowance received, and divide by the total lease term in months to produce a monthly average. This gives you the landlord-concession-adjusted cost on a per-square-foot basis.
The second layer adjusts for the growth-space absorption. Here you calculate effective rent per occupied square foot by dividing the total rent obligation — again net of concessions — by the total occupied square feet integrated over the lease term. This second figure will always be higher than the first during the absorption period, and the gap between the two numbers is what growth space actually costs the organization beyond the nominal rent.
Presenting both figures to decision-makers matters. The first tells the real estate team how the deal compares to market. The second tells finance how much the organization is paying per productive seat or productive square foot over time. Both are correct; they answer different questions.
Modeling the Lease Net Present Value with Scenario Weighting
It translates the entire cash flow stream — rent payments, free rent offsets, tenant improvement proceeds, sublease income, and transaction costs — into a single present value figure that can be compared across options or used as the basis for a build-versus-lease or lease-versus-expand decision.
Corporate real estate teams often use the organization's weighted average cost of capital, though some advisers use a risk-adjusted rate that is slightly higher to account for the illiquidity of the lease obligation. The choice of discount rate is a judgment call that should be documented and consistent across options being compared.
This weighted figure is the number the organization is actually committing to in expectation. The range between the downside and upside NPVs is the risk the organization is accepting.
Structuring the Termination Option Analysis
The logic is straightforward: if the absorption scenario does not materialize, the organization needs an exit mechanism that is less disruptive than a sublease and less costly than a lease buyout negotiated from a position of weakness.
That penalty can be estimated by asking for the landlord's unamortized cost schedule, or by modeling it independently based on market norms.
Understanding this resistance helps you negotiate more effectively. Offering a higher termination penalty in exchange for an earlier exercise window, or a longer notice period in exchange for a lower penalty, gives the landlord certainty while preserving optionality for the tenant.
The trade-off belongs in the model as a sensitivity, not resolved by convention.
Addressing Build-Out Timing and Capital Cost Allocation
The model should capture whichever structure applies and reflect the time value of the allowance accordingly.
Integrating Lease Economics Into the Portfolio Decision
A growth-space commitment sits inside a portfolio of existing obligations, planned dispositions, and future requirements. Evaluating the lease economics of a single growth-space deal without reference to the broader portfolio can produce a decision that appears efficient in isolation but creates compounding obligations at the portfolio level.
Presenting the Model to Finance and Leadership
The model is only as useful as its communication. A growth-space NPV analysis that lives in a spreadsheet accessed by three people does not help leadership make a confident decision. Translating the technical lease economics into the language of business outcomes is a distinct part of the work, not an afterthought.
These three figures answer the question leadership is actually asking — "what are we committing to, and what does it cost us if the hiring plan misses?" They do not require the audience to understand discounted cash flow methodology to interpret.
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