How to Calculate NNN Charges for a Tenant, Step by Step

To calculate NNN charges, add the property’s taxes, insurance, and CAM, apply the adjustments the lease allows, and multiply by the tenant’s pro-rata share. The adjustments are where a quick per-square-foot estimate and the correct figure part ways.

The inputs

A 120,000 rentable square foot center, 80% occupied. The tenant leases 9,000 rentable square feet.

Real estate taxes            $336,000
Building insurance            $96,000
CAM                          $360,000   (of which $150,000 is variable)
Lease terms                  gross-up CAM to 95%, 4% admin fee on CAM only

Step 1: Pro-rata share

9,000 RSF / 120,000 RSF = 7.50%

Use rentable area on both sides, and use the building denominator the lease specifies. The pro-rata share article covers why the denominator choice moves every tenant’s number.

Step 2: Gross up variable CAM

Only the variable portion of CAM moves with occupancy, so only that portion is grossed up:

$150,000 x (0.95 / 0.80) = $178,125     uplift $28,125
CAM after gross-up = $360,000 + $28,125 = $388,125

Taxes and insurance are not grossed up. They do not fall when the building empties. Gross-up explained covers the common mistakes.

Step 3: Admin fee

This lease applies a 4% administrative fee to CAM only:

$388,125 x 4% = $15,525     CAM with fee = $403,650

Some leases apply the fee to all three nets, some exclude taxes and insurance, and some cap it. Read the clause rather than carrying one rule across a portfolio.

Step 4: Tenant share of each net

Net	Property total	Tenant share (7.50%)
Taxes	$336,000	$25,200.00
Insurance	$96,000	$7,200.00
CAM with gross-up and fee	$403,650	$30,273.75
Total	$835,650	$62,673.75

Monthly estimate: $62,673.75 / 12 = $5,222.81.

Keep the three nets separate on the tenant’s statement. When a tenant asks why the charge moved, “taxes rose 9% after reassessment” is an answer. A single blended number is not.

Why the quick building-wide rate undercharges

The shortcut many firms use:

($336,000 + $96,000 + $360,000) / 120,000 RSF = $6.60 per SF
9,000 RSF x $6.60 = $59,400

That is $3,273.75 short of what this lease allows, because it skips gross-up and the admin fee. Multiply that across every suite in a partly vacant center and the landlord absorbs a meaningful share of operating cost it was entitled to recover.

The shortcut can also overcharge. A tenant with a CAM cap, a negotiated exclusion, or a fixed share would be billed more than its lease permits. Either way, the reconciliation exposes it.

From estimate to reconciliation

The figure above is the estimate, built from the budget. After year end the same calculation runs on actual costs, actual occupancy, and the lease’s base year or cap if it has one, and the difference is trued up. The triple net lease guide walks through that annual cycle.

Run your own numbers in the NNN occupancy cost calculator, or see how NNN lease management keeps each lease’s adjustments attached to its share.