What is TMI / Additional Rent in a commercial lease?

TMI (Taxes, Maintenance, Insurance), also called Additional Rent or Operating Costs, is a commercial tenant's proportionate share of a building's operating costs, reconciled each year against the lease.

How do I know if my Ontario TMI reconciliation is overcharged?

Common overcharges: capital projects billed as operating costs, management fees on the wrong base, gross-up applied to fixed costs like taxes, and HST errors. TMI Proof checks each line against your lease.

Is the TMI check free?

Yes. The first check is free. Upload your lease and TMI / Additional Rent statement and TMI Proof flags what doesn't reconcile, each finding tied to the exact lease clause.

For Ontario commercial tenants

Is your TMI bill correct?

Your year-end TMI / Additional Rent (Taxes, Maintenance, Insurance) is one of the most over-billed lines in a commercial lease. Upload your lease and statement. We check every charge against your lease terms, HST included, and flag what doesn’t reconcile. Every flag cites the exact clause.

Not a fight with your landlord: a calm CRA-compliance reconciliation. Additional Rent carries 13% HST, so getting it right keeps your input-tax-credit filing clean.

Check my TMI, free →See a worked sample: $6,185 flagged →

Free checkNo accountEvery finding cites your lease clause

A worked example

See exactly what you’d get

A sample Ontario plaza reconciliation, run through the check: the findings, then a ready-to-send letter. This is a demo, not your bill.

ExampleA sample Ontario plaza reconciliation (not your bill). Your own check runs on your lease.

What the check flagseach item cites the lease clause

Parking-lot repaving (capital project) doesn't belong on the bill

Your lease excludes it (Sec 7.2(a) (capital excluded)). It isn't a shared cost the tenant owes, so take it off.

R20 · Ironclad · Lease Sec 7.2(a) (capital excluded)

$6,000.00

over-billed

HST over-charged on your TMI

HST should be 13% of the net additional rent ($18,500.00) = $2,405.00, but the statement shows $2,590.00, a $185.00 over-charge to correct.

R26 · Ironclad · Lease GST/HST on additional rent (CRA, Excise Tax Act)

$185.00

over-billed

Amounts shown are building-level pool figures; what lands on your bill is your proportionate share of the pool, but a wrongly-included item (like the capital repaving above) inflates every tenant’s share until it’s removed.

Before you claim the HST back

two things to check with your accountant

Getting the HST back is not automatic

You can recover the HST on your Additional Rent as an input tax credit only if you are a GST/HST registrant and use the space for taxable (commercial) activity. If your use is exempt or mixed, recovery may be partial or nil, so do not assume the HST always washes out. Confirm your ITC position with your accountant. This is general information, not tax advice.

Watch for HST already inside the operating costs

If the landlord paid a vendor $100 + $13 HST = $113 and recovered that $13 as their own input tax credit, the cost passed on to you should be the net $100, not $113. Otherwise, when HST is added to your TMI total, you pay the tax twice. Ask the landlord to confirm operating costs are billed net of any recoverable HST.

Before your deadline passes

a legal time limit, separate from the lease audit window

Your legal deadline may be shorter than you think

Separate from the audit window in your lease, a claim to recover overpaid additional rent in Ontario is generally subject to a limitation period (often about two years from when you knew or should have known of the overcharge, and your lease may make it shorter). Do not assume you have years to act. Confirm your actual deadline with a lawyer. This is general information, not legal advice.

Your reconciliation request (draft)

Draft · review with your accountant before sending

September 05, 2026

To: [Your landlord / property manager]
From: [You, tenant]

Re: Sample Ontario plaza TMI 2025 (illustrative): request to reconcile Additional Rent (TMI)

In reconciling my year-end Additional Rent (TMI) statement against the lease for my records, a few items don’t appear to reconcile. Because Additional Rent carries HST, these affect my input-tax-credit filing (to the extent I am entitled to claim it) and the records I’m required to keep for CRA, so I’d like to line them up before I close my books:

Parking-lot repaving (capital project) doesn't belong on the bill, $6,000.00 (Lease Sec 7.2(a) (capital excluded))
HST over-charged on your TMI, $185.00 (Lease GST/HST on additional rent (CRA, Excise Tax Act))

Total in question: $6,185.00.
Could you please send the supporting invoices for these items and, where warranted, a corrected statement, so my HST filing reconciles. Each item notes the lease section it relies on. Thanks very much, happy to hop on a call.

Regards,
[You]

We don’t invent overcharges

Every flag cites the exact lease clause it turns on, so your request to the landlord is grounded, not a guess.

Reproducible to the cent

Calculated deterministically from your statement and lease, HST included. Re-run it and the numbers match.

Check my own TMI, free →

Free, no account. Your lease and statement are deleted the moment they’re read, never stored or shared.

New to TMI? Read the Ontario TMI & Additional Rent guide: what it is, the overcharges to watch for, and your rights as a tenant.

A starting point for review, not legal, accounting, or tax advice. Confirm each item against your lease and with your accountant before acting. Sample figures are illustrative.