Commercial Real Estate Underwriting: A Complete Guide
Underwriting a commercial property is the process of evaluating its financial performance to determine whether it justifies a given purchase price, loan amount, or investment decision. Done correctly, it is the single most important analytical step in any CRE transaction.
The Income Approach Explained
The income approach values a property based on the income it produces — not what comparable properties sold for (sales comparison) or what it would cost to rebuild (cost approach). For income-producing commercial real estate, the income approach is almost always the primary valuation method.
The core sequence is:
Gross Potential Rent
− Vacancy & Credit Loss
= Effective Gross Income (EGI)
− Operating Expenses
= Net Operating Income (NOI)
÷ Cap Rate
= Estimated Value
Gross Potential Rent
− Vacancy & Credit Loss
= Effective Gross Income (EGI)
− Operating Expenses
= Net Operating Income (NOI)
÷ Cap Rate
= Estimated Value
Step 1 — Gross Potential Rent
Start with the maximum possible rent if every unit or space were occupied at market rate for the full year. For a multi-tenant retail strip, this means summing all lease line items at their current or market rents.
Key question: Are current rents at, above, or below market? Below-market leases reduce actual income and should be flagged in your BPS cap rate adjustment.
Step 2 — Vacancy and Credit Loss
No property runs at 100% occupancy indefinitely. Apply a vacancy rate that reflects:
- Historical occupancy for the subject property
- Submarket vacancy trends
- Lease rollover risk (upcoming expirations)
- Tenant credit quality
A common default is 5% for stabilized assets in strong markets, rising to 10–15% for value-add or tertiary market properties.
Step 3 — Operating Expenses
Operating expenses typically run 35–55% of EGI for most commercial property types. They include:
| Expense Category | Notes |
|---|---|
| Property taxes | Verify actual tax bill; reassessment risk post-sale |
| Insurance | Obtain current quote; older buildings cost more |
| Property management | 4–8% of EGI for professional management |
| Maintenance & repairs | Budget $0.50–$2.00/SF depending on age and condition |
| Utilities (common area) | Actual bills preferred over estimates |
| Reserves for replacement | $0.10–$0.25/SF annually |
Do not include debt service in operating expenses. NOI is a pre-financing metric.
Step 4 — Net Operating Income
NOI is the number lenders and appraisers use as their starting point. It is also the number that, divided by the cap rate, produces your value estimate.
Protect your NOI calculation by:
- Using trailing 12-month actuals where available
- Stress-testing with a proforma NOI that normalizes for one-time items
- Documenting every assumption in your analysis
Step 5 — Value Guidance
Divide your stabilized NOI by the appropriate cap rate to arrive at a value guidance number. This is not an appraisal — it is an analytical benchmark that tells you whether the asking price is defensible.
Value Guidance = NOI ÷ Cap Rate
Value Guidance = NOI ÷ Cap Rate
If the seller's asking price implies a cap rate materially below what the market supports, you have identified a pricing gap that needs to be addressed in negotiation or due diligence.
How 1DIAS Streamlines the Process
The 1DIAS Underwriter executes this entire sequence in real time. Enter average monthly rent, unit count, vacancy percentage, total annual expenses, and cap rate — and the platform instantly calculates:
- Total monthly rents
- Annual gross rents
- Vacancy amount
- Adjusted gross income
- Net operating income
- Value guidance
Every analysis can be saved to Deal History, exported as a PDF, and shared with clients or partners via a unique link.
Common Underwriting Mistakes
- Using asking rents instead of actual rents — always verify with rent rolls
- Ignoring expense reimbursements — NNN leases shift expenses to tenants; gross leases do not
- Applying national cap rate averages — local submarket data is always more accurate
- Forgetting capital expenditure reserves — deferred maintenance destroys NOI post-acquisition
- Not stress-testing vacancy — model a 10% vacancy scenario even for stabilized assets
Run your next underwriting analysis in under two minutes with 1DIAS Underwriter [blocked].