NNN Property Tax Proration and True-Ups: A Landlord's Guide
Property tax is usually the largest single line item in an NNN tenant's pass-through obligations. It's also one of the most frequently miscalculated — particularly in mid-year situations like closings, tenant changeovers, and assessment appeals.
This guide covers how property tax proration works in NNN leases, when true-ups are required, and how to handle the year-end reconciliation without leaving money on the table or picking a fight with a tenant over math they can prove wrong.
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How Property Tax Works in a NNN Lease
In a standard triple-net lease, the tenant pays their pro-rata share of the property's real estate taxes. For a single-tenant property, that's typically 100%. For a multi-tenant property, it's the tenant's proportionate share based on square footage (or sometimes occupied square footage, depending on the lease).
The timing problem: Property taxes are assessed on a schedule that doesn't always align neatly with lease commencement dates, year-ends, or tenant changeovers. Bills come annually, semi-annually, or quarterly depending on the jurisdiction. Your lease year and the tax year may not match.
Most NNN leases handle this with estimated monthly payments. Tenants pay a monthly estimate of their tax obligation along with base rent, and the landlord true-up at year-end when the actual tax bill is known.
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The Estimate-and-True-Up Cycle
Estimates: At the start of each lease year (or calendar year, depending on your lease structure), you set the estimated monthly tax contribution based on last year's actual tax bill plus any anticipated increase (assessment increases, mill rate changes, or known appeal resolutions).
This estimate should be communicated to the tenant in writing, typically 30-60 days before the new year. Some leases specify the exact timing and form. If you don't notify on time, some tenants will argue they can keep paying the prior year's estimate until you do.
True-up timing: Once you receive and pay the actual tax bill, you reconcile. Actual taxes paid vs. estimated taxes collected = credit back to tenant (over-collected) or invoice to tenant (under-collected).
For most commercial leases this reconciliation happens alongside the annual CAM reconciliation, but property tax and CAM are typically separated into distinct line items in the reconciliation statement.
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Mid-Year Closings: Proration at Acquisition
If you acquire a NNN property mid-year, the property tax proration at closing is one of the most important financial adjustments in the sale.
How it typically works:
The seller is responsible for taxes accrued up to the closing date; the buyer takes over from the closing date forward. Since tax bills are often paid in arrears (you pay 2025 taxes in 2026), the proration is usually a credit from seller to buyer at closing.
The proration calculation uses either:
- The prior year's actual tax bill (most common) — prorated to closing date
- An estimated current-year tax bill — if current year taxes are already known or can be estimated
Post-closing true-up: When the actual tax bill arrives after closing, there may be a difference from the closing proration. Some purchase agreements include a post-closing true-up provision requiring the parties to settle the difference. Others treat the closing proration as final.
What landlords miss at acquisition:
- Whether the seller was collecting tax estimates from tenants (and whether those estimates were adequate)
- Whether there's an outstanding appeal that could change the final bill
- Whether the closing proration used an outdated base figure
Review the rent roll and estoppel certificates at closing to understand exactly what the tenant has been paying and what the current estimate is.
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Tenant Changeovers: Proration Within the Lease Year
When a tenant turns over mid-year — lease expiration, early termination, or default — the outgoing tenant's obligation needs to be settled and the incoming tenant's obligation set up correctly.
Outgoing tenant: Entitled to (or obligated for) a proration of the annual tax based on their occupancy period. If you collected monthly estimates and the tenant was there for 7 months, they owe 7/12 of their annual share — adjusted for actual vs. estimated taxes when the bill arrives.
Incoming tenant: If the lease is structured with monthly estimates, set the estimate based on the current or anticipated actual tax bill. Don't assume the outgoing tenant's rate was right.
Documentation matters: Keep a clear record of what estimates were collected from each tenant, the proration calculation at turnover, and any amounts credited or invoiced. This becomes important when you're doing end-of-year reconciliation and have two tenants on the same space for the same tax year.
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Assessment Appeals: Who Benefits, Who Pays
Assessment appeals are common in commercial real estate — you challenge the assessor's value, potentially get a reduced assessment, and lower taxes for future years. What happens with the refund and the appeal costs in a NNN lease is often misunderstood.
Typical lease structure:
The landlord has the right (sometimes the obligation) to appeal assessments. If the appeal results in a refund for prior years, that refund is credited back to tenants in proportion to their original overpayment — net of appeal costs.
Common issues:
- Who controls the appeal? Most leases give the landlord sole discretion. Some tenants negotiate the right to demand an appeal if the assessment exceeds a certain amount.
- What happens to appeal costs? Typically deducted from any refund before distribution, or treated as an allowable CAM expense (depending on whether the lease includes assessment appeal costs in the definition of operating expenses).
- Timing of credits: A successful appeal in 2026 covering the 2024 tax year means you're crediting tenants who may have left. You need to track down former tenants and issue credits, or (if the lease is silent on departure) consult your attorney.
- Assessment increases: If an appeal fails and the assessor counter-proposes a higher value, tenants will owe more. Make sure the lease is clear about whether appeal risk (increased assessment) falls on the landlord or flows through to tenants.
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Year-End Reconciliation: What to Include
The property tax line in your annual reconciliation should show:
1. Total actual taxes paid for the reconciliation period (attach copies of tax bills) 2. Tenant's share percentage (from the lease — usually pro-rata by square footage) 3. Tenant's actual obligation = total taxes x share % 4. Total estimated payments collected from tenant during the year 5. Balance due or credit owed = obligation minus payments collected
For multi-tenant properties, also show:
- Total building taxes
- Total leasable square footage
- Each tenant's square footage and proportionate share
Attach the tax bills. Tenants with audit rights will ask for them anyway, and having them in the reconciliation package reduces back-and-forth.
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Where Things Go Wrong
Using the wrong proration fraction: A partial-year tenant or a mid-year acquisition needs a daily or monthly proration. Applying an annual share percentage to a partial-year occupant overstates their obligation.
Not accounting for appeal credits: If you won an appeal covering a prior year, the credit to tenants needs to flow through the reconciliation — or you're retaining money that belongs to them.
Mismatched fiscal/calendar years: If your lease runs on a fiscal year but the tax assessor bills on a calendar year, your reconciliation period and the tax period don't align perfectly. You may need to prorate taxes across two reconciliation years.
Not tracking mid-year estimate changes: If you changed the estimated monthly payment mid-year (due to a supplemental assessment or appeal resolution), make sure the reconciliation reflects the correct total estimates collected — not just 12 months at the original rate.
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Practical Workflow
The property tax reconciliation is one component of the broader NNN year-end process. Keeping it clean requires:
- A tracking sheet for each property showing the tax bill amounts, payment dates, and tenant estimate schedules
- A running total of estimates collected from each tenant (this is often where the error is — the reconciliation software or spreadsheet uses the current estimate rate extrapolated, not actual amounts collected)
- Copies of all tax bills filed by property and tax year
- A log of any appeals — status, expected resolution, impact on current year estimates
Landlords managing several properties often consolidate this into a year-end reconciliation process that runs simultaneously with CAM. The operational workflow — collecting invoices, checking allocations, issuing statements — is similar enough that they're typically handled together.
For a broader view of NNN lease financial management, see our guides on CAM reconciliation and preventing CAM reconciliation disputes.