Lease Modelling Mechanics
Executive Summary
Key Takeaways
- ✓ A lease's cash flow impact is determined by more than its headline rent figure, free rent or incentive periods, tenant improvement allowances, and renewal or termination options each affect the actual cash the landlord receives and when.
- ✓ Free rent or incentive periods should be modelled as an explicit zero- or reduced-rent period at lease commencement, not netted into a single blended "effective rent" figure that obscures the actual cash timing.
- ✓ Tenant improvement allowances, capital the landlord funds toward tenant fit-out, should be modelled as an upfront cash outflow at or near lease commencement, distinct from ongoing operating expenditure.
- ✓ Renewal options should be modelled with an explicit assumption about exercise probability and the rent basis on renewal, since an option renewing at a below-market fixed rent carries different risk than one renewing at open market rent.
- ✓ Early termination (break) options held by the tenant should be modelled as a risk-weighted possibility at the break date, feeding into the same void and re-leasing cost treatment as a natural lease expiry.
Institutional Definition¶
A lease's actual cash flow impact is determined by more than its headline rent figure — free rent or incentive periods, tenant improvement allowances, and renewal or termination options each affect the actual cash the landlord receives and when, and should be modelled explicitly rather than netted into a simplified effective rent figure. This guide addresses the lease-level building blocks that feed the lease-level rent roll described in Commercial Office Model Structure and applicable across property types.
Free Rent and Incentive Periods¶
Free rent or other incentive periods at lease commencement should be modelled as an explicit zero- or reduced-rent period, not netted into a single blended "effective rent" figure that obscures the actual cash timing. A lease with three months free rent at commencement has a materially different early cash flow profile than one paying a slightly lower rent throughout the term, even where the two produce a similar average, and a cash flow model needs the actual timing rather than an average.
Tenant Improvement Allowances¶
A tenant improvement allowance, capital the landlord funds toward the tenant's fit-out in exchange for the lease commitment, should be modelled as an upfront cash outflow incurred at or near lease commencement, distinct from ongoing operating expenditure. Folding this cost into a general capital expenditure line without tying it to the specific lease event that triggers it obscures the true cost of securing that tenant.
Renewal Options¶
Lease renewal options should be modelled with an explicit assumption about the probability the tenant exercises the option and the rent basis that applies on renewal, a fixed, pre-agreed rent, or open market rent at the renewal date. A below-market fixed renewal rent carries materially different risk to the landlord than an open-market renewal, and treating all renewal options as equivalent conceals that difference.
Early Termination (Break) Options¶
A tenant's early termination or break option should be modelled as a risk-weighted possibility at the break date, typically with a stated exercise probability or scenario assumption, feeding into the same void and re-leasing cost treatment described in Commercial Office Model Structure that applies at a natural lease expiry, if the break is assumed exercised.
Common Structural Errors¶
Blended effective rent. Netting free rent into a single average rent figure rather than modelling the actual zero- or reduced-rent period explicitly misstates near-term cash flow timing.
Tenant improvement allowance folded into general capex. Failing to tie tenant improvement cost to the specific lease event that triggers it obscures the true cost of securing that tenant.
Uniform renewal treatment. Treating every renewal option as equivalent regardless of its actual rent basis conceals materially different landlord risk between a fixed-rate and open-market renewal.
Audit Checks¶
Free rent timing check. Confirm free rent or incentive periods are modelled as an explicit cash flow timing item, not blended into an average rent figure.
Tenant improvement cost trace. Confirm tenant improvement allowances are tied to specific lease events, modelled as upfront capital outflow.
Renewal and break option check. Confirm renewal and break options carry explicit exercise probability and rent basis assumptions.
Best Practices¶
| Best Practice | Why It Matters |
|---|---|
| Model free rent as an explicit zero- or reduced-rent period, not a blended average | Preserves accurate near-term cash flow timing |
| Model tenant improvement allowances as upfront capital tied to the specific lease | Keeps the true cost of securing each tenant visible and traceable |
| Assign explicit exercise probability and rent basis to renewal options | Distinguishes below-market from open-market renewal risk |
| Risk-weight tenant break options and link them to void/re-leasing cost treatment | Represents genuine lease-continuation uncertainty rather than assuming full-term certainty |
Further Reading¶
- RICS, Valuation — Global Standards (Red Book), Royal Institution of Chartered Surveyors
- Appraisal Institute, The Appraisal of Real Estate
Continue Reading¶
Prerequisites¶
- Real Estate Financial Modelling — the parent pillar
- Commercial Office Model Structure
Related Technical Guides¶
Related Products¶
How OXXON tests thisRun a free structural check with FMAE
Frequently Asked Questions
Why shouldn't free rent be netted into a single blended effective rent figure?
Because netting obscures the actual timing of cash the landlord receives, a lease with three months free rent at commencement has a materially different early cash flow profile than one paying a slightly lower rent throughout the term, even if the two produce a similar blended average, and a cash flow model needs the actual timing, not just the average.
How should a tenant improvement allowance be modelled?
As an upfront cash outflow incurred at or near lease commencement, distinct from ongoing operating expenditure, since it is a capital cost the landlord funds toward the tenant's fit-out in exchange for the lease commitment, not a recurring operating cost.
How should lease renewal options be modelled?
With an explicit assumption about the probability the tenant exercises the option and the rent basis that applies on renewal (a fixed pre-agreed rent, or open market rent at the renewal date), since a below-market fixed renewal rent carries materially different risk to the landlord than an open-market renewal.
How should a tenant's early termination (break) option be modelled?
As a risk-weighted possibility at the break date, typically with a stated exercise probability or scenario assumption, feeding into the same void and re-leasing cost treatment that applies at a natural lease expiry if the break is assumed exercised.
What is the risk of modelling only headline rent without these mechanics?
The model overstates near-term cash flow (by ignoring free rent), understates upfront capital requirements (by ignoring tenant improvement allowances), and fails to represent genuine uncertainty around lease continuation (by ignoring renewal and break option risk), each of which can materially distort both near-term cash flow and the asset's valuation.
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