Net Operating Income (NOI), Explained Simply

Net operating income (NOI) is what a property earns from operations in a year: its gross operating income minus its operating expenses. It leaves out loan payments, depreciation, capital expenditures and income taxes, so it measures the building itself rather than the owner’s finances.

NOI is the number almost everything in commercial real estate is built on. Cap rates use it, lenders test it and buyers argue about it. This guide covers the formula, what counts as an operating expense, a worked example, and how NOI differs from cash flow. Then we’ll show how the idea shows up when you manage buildings in CRE Tycoon.

The net operating income formula

NOI = Gross operating income − Operating expenses

That’s the whole formula. The skill is in getting each side right.

Gross operating income

Most analysts build up to gross operating income in a few steps:

1. Potential gross income: all the rent the building would collect if every space were leased at its scheduled rent.
2. Minus vacancy and credit loss: an allowance for empty space and tenants who don’t pay.
3. Plus other income: parking, storage, laundry, signage, expense reimbursements from tenants and similar items.

The result is gross operating income (sometimes called effective gross income): the money you realistically expect to come in.

Operating expenses

Operating expenses are the regular costs of running the property. Typical examples:

• Property taxes
• Insurance
• Repairs and routine maintenance
• Utilities the owner pays
• Property management fees
• Landscaping, cleaning, security and trash removal
• Administrative costs tied to the property

What NOI leaves out

This is where most beginners go wrong. The following items are not operating expenses and don’t come out of NOI:

• Debt service. Mortgage principal and interest depend on how the owner financed the deal, not on how the building performs.
• Depreciation. It’s an accounting and tax deduction, not cash spent running the property.
• Capital expenditures. Big, occasional investments like a new roof, a parking lot replacement or a major system upgrade are tracked separately.
• Income taxes. These belong to the owner, not the property.

Some owners deduct a yearly “reserve for replacements” in their NOI to account for capital needs in a smoother way. Practices differ, so when you compare two buildings, check whether both NOI figures were built the same way.

Key takeaway: NOI describes the property, not the owner. Financing, tax strategy and one-off capital projects are handled after NOI.

A worked NOI example

Here’s a simple illustrative example with round numbers. It isn’t based on any real market.

Picture a small office building with ten suites.

Line	Amount (per year)
Potential gross income (10 suites fully leased)	$200,000
Less vacancy and credit loss	−$20,000
Plus other income (parking)	+$10,000
Gross operating income	$190,000
Property taxes	−$25,000
Insurance	−$10,000
Repairs and maintenance	−$15,000
Utilities (owner-paid)	−$12,000
Management	−$8,000
Total operating expenses	−$70,000
Net operating income	$120,000

Now suppose the owner also has a mortgage costing $80,000 a year and plans to spend $15,000 replacing a roof section. Neither of those touches NOI. NOI is still $120,000.

NOI vs cash flow

Cash flow is what actually lands in the owner’s pocket. A simple version:

Cash flow before taxes = NOI − Debt service − Capital expenditures

Using the example above: $120,000 − $80,000 − $15,000 = $25,000.

That’s a big gap from $120,000. It’s also why two owners of identical buildings can have very different experiences. One with no loan keeps much more each year. One with a large loan keeps less, but may have bought with far less of their own money.

Why lenders care about NOI

Lenders look at the debt service coverage ratio (DSCR):

DSCR = NOI ÷ Annual debt service

In the example, $120,000 ÷ $80,000 = 1.5. That means the building’s NOI covers its loan payments one and a half times. Lenders set their own minimum DSCR, and a weaker ratio means less room if income dips. We cover this more in our refinancing explainer.

Why buyers care about NOI

NOI feeds straight into value through the cap rate:

Value = NOI ÷ Cap rate

At an illustrative 8% cap rate, $120,000 of NOI suggests a value of $1,500,000. If the owner raises NOI by $10,000 a year, the same cap rate implies a value about $125,000 higher. That’s why investors care so much about every line of income and expense. Our cap rate guide walks through this in detail.

How owners increase NOI

There are only two levers: raise income or cut operating costs. In practice that looks like:

• Reducing vacancy. Filling empty space is often the biggest single lever.
• Bringing rents up to market as leases renew.
• Adding other income such as paid parking or storage.
• Controlling expenses through better contracts, energy savings or appealing a tax assessment.
• Improving the property so it attracts better tenants, which usually takes capital spending first.

Each lever has trade-offs. Pushing rents too hard can raise vacancy, and cutting maintenance can save money today and cost much more later.

Common NOI mistakes

• Using potential rent instead of realistic collected income.
• Forgetting vacancy entirely.
• Treating a seller’s projected (pro forma) NOI as if it were already happening.
• Subtracting the mortgage and calling the result NOI.
• Ignoring capital needs because they’re “not in NOI.”
• Comparing two buildings whose NOI was calculated differently, such as one that deducts a replacement reserve and one that doesn’t.

Trailing vs projected NOI

You’ll often see two versions of NOI on the same property. Trailing NOI (sometimes called T-12, for the trailing twelve months) is based on what the building actually earned and spent over the past year. Projected or pro forma NOI is an estimate of what it could earn, often assuming more leasing or higher rents. Both are useful, but they answer different questions. Buyers and lenders usually lean on trailing figures and treat projections with healthy skepticism until they’re backed by signed leases.

How NOI shows up in CRE Tycoon

CRE Tycoon is our free commercial real estate tycoon game. You start as a broker with $100,000, then buy buildings and fill them with tenants over a 10-year career. The game lists NOI among its “real CRE math, simplified” features, alongside cap rates, loans, refinancing and market cycles.

Here’s where thinking in NOI terms helps you:

• The Deal Sheet. Before you buy, it shows what you put in and what the building pays each month. Asking “what does this property really earn?” is the NOI mindset in a single glance.
• Leasing up. Filling a building with tenants is the game’s version of cutting vacancy, the biggest lever in the real world too.
• Business plans and upgrades. Plans range from a quick Fix-Up to a full Redevelop, and bigger plans pay more and carry more risk. That’s the same trade-off as spending capital to raise income.
• Refinancing. Real lenders size loans partly on NOI, so a building earning more can support more borrowing. In the game, refinancing lets you pull out cash to fund your next move.

You don’t need a spreadsheet to play. But once you think “income minus running costs, before the loan,” you’ll read buildings faster. For the full rundown, see our how to play CRE Tycoon guide, then try a career and see what your portfolio is earning by month 120.

FAQ

What is net operating income in real estate?

Net operating income is a property’s gross operating income minus its operating expenses. It measures what the building itself earns in a year before loan payments, depreciation, capital expenditures and income taxes.

Does NOI include mortgage payments?

No. Debt service is left out of NOI on purpose, so the number describes the property rather than the owner’s financing. Loan payments come out afterward when you calculate cash flow.

Is NOI the same as cash flow?

No. Cash flow before taxes is roughly NOI minus debt service and capital spending. A property can have strong NOI and weak cash flow if it carries a large loan or needs major repairs.

Why is NOI important?

NOI drives value in commercial real estate. Cap rates, lender tests like the debt service coverage ratio, and most valuation methods all start from it.

This article is for education and entertainment, not financial advice.