Real Estate Math in Ontario: Every Formula You Need (2026)
The complete real estate math reference for the Humber exam — commission, mortgage, property tax, GST/HST, area, and capitalization formulas with worked examples.
Real Estate Math in Ontario: Every Formula You Need
Math is the single most common reason students fail the Humber real estate exams. The math itself is straightforward grade 10 material, but the format is unforgiving: scenario-based word problems where you have to identify the right formula, extract the right numbers, and execute the calculation in under 2 minutes. This guide is the complete formula reference, with worked examples for each.
Key Takeaways
- Real estate math on the Humber exam is not advanced. It is grade-10 level percentages, ratios, and basic algebra applied to real estate scenarios.
- 15 to 20% of pre-registration exam questions involve a calculation. Course 4 (Commercial) is the math-heaviest at roughly 30%.
- The difficulty is in scenario translation, not raw computation. You have to figure out which formula applies before you can apply it.
- A basic non-programmable calculator is allowed. Bring one. Phone calculators are not permitted.
1. Commission
The most-tested calculation. Two flavours: total commission and per-side commission after brokerage splits.
Formula:
Commission = Sale Price × Commission Rate
Worked example: A home sells for $850,000. The total commission rate is 5%, split 2.5% to the listing brokerage and 2.5% to the buyer brokerage.
- Total commission: $850,000 × 0.05 = $42,500
- Listing-side commission: $850,000 × 0.025 = $21,250
- Buyer-side commission: $850,000 × 0.025 = $21,250
If the listing agent has a 70/30 split with their brokerage:
- Brokerage portion: $21,250 × 0.30 = $6,375
- Agent portion: $21,250 × 0.70 = $14,875
The agent then remits HST collected on their portion if registered, but the take-home before tax on this transaction is roughly $14,875.
For more on what agents actually earn, see our breakdown of Ontario real estate agent salaries.
2. Property Tax Pro-Ration at Closing
When a property changes hands mid-year, the buyer reimburses the seller for the portion of property tax already paid that covers the buyer's ownership period. (Or vice versa if tax is unpaid.)
Formula:
Daily tax = Annual property tax ÷ 365
Adjustment = Daily tax × number of days the buyer owns in the current tax year
Worked example: Annual property tax is $4,380. Closing date is October 1. The seller has already paid the full year.
- Daily tax: $4,380 ÷ 365 = $12.00 per day
- Days from October 1 to December 31 (inclusive): 92 days
- Buyer owes seller at closing: $12.00 × 92 = $1,104.00
The credit shows up on the closing statement as a buyer-side debit and a seller-side credit.
3. Mortgage Qualifying Ratios: GDS and TDS
The Gross Debt Service (GDS) and Total Debt Service (TDS) ratios determine whether a buyer qualifies for a mortgage. The 2026 stress-test rules cap GDS at roughly 39% and TDS at roughly 44% for most A-lender mortgages.
Formulas:
GDS = (Mortgage payment + Property tax + Heating cost + 50% of condo fees) ÷ Gross monthly income
TDS = GDS components + All other monthly debt payments ÷ Gross monthly income
Worked example: Buyer has gross income of $90,000 per year ($7,500/month). Monthly mortgage payment $2,200, property tax $400, heating $150, condo fees $0, plus a car loan at $450/month and student loan at $300/month.
- GDS = ($2,200 + $400 + $150) ÷ $7,500 = $2,750 ÷ $7,500 = 36.7% (passes the 39% cap)
- TDS = ($2,750 + $450 + $300) ÷ $7,500 = $3,500 ÷ $7,500 = 46.7% (fails the 44% cap)
Even though GDS qualifies, TDS does not. This buyer would need to reduce other debt or increase income to qualify for this property at this loan size.
4. Mortgage Payment from Mortgage Factor
The Humber program uses a mortgage payment factor table rather than the full amortization formula. The factor represents the monthly payment per $1,000 of mortgage at a given rate and amortization.
Formula:
Monthly payment = Mortgage amount ÷ 1,000 × Mortgage factor
Worked example: $640,000 mortgage at 5.49% with 25-year amortization. The mortgage factor for 5.49% / 25 years is approximately 6.1052.
- Monthly payment: $640,000 ÷ 1,000 × 6.1052 = 640 × 6.1052 = $3,907.33
You will not need to memorize the factor table; the exam typically provides the relevant factor in the question. You need to apply it correctly.
5. Cap Rate (Capitalization Rate)
Used heavily in Course 4 (Commercial). The cap rate measures a property's annual return based on net operating income.
Formula:
Cap Rate = Net Operating Income ÷ Property Value
Or rearranged to solve for value:
Property Value = NOI ÷ Cap Rate
Worked example: A commercial property generates $180,000 in gross rents. Operating expenses (property tax, insurance, maintenance, management) total $54,000. Comparable cap rate in the market is 6.5%.
- NOI = $180,000 − $54,000 = $126,000
- Property Value = $126,000 ÷ 0.065 = $1,938,461
Cap rate questions almost always require you to calculate NOI first by subtracting operating expenses from gross income. Vacancy is sometimes included as a separate deduction; read the question carefully to know whether it has been factored in already.
6. Gross Income Multiplier (GIM)
A simpler valuation method, used as a quick sanity check on commercial value.
Formula:
Property Value = Gross Annual Income × GIM
GIM = Property Value ÷ Gross Annual Income
Worked example: Property generates $96,000 in gross annual rent. Comparable GIM in the market is 9.5.
- Property Value = $96,000 × 9.5 = $912,000
GIM is faster than cap rate but ignores expenses, so it is less accurate.
7. GST/HST on New Construction
In Ontario, new home purchases are subject to 13% HST. The HST rebate partially refunds this for purchases under specific thresholds.
Formula:
HST = Pre-tax price × 0.13
Total purchase price = Pre-tax price × 1.13
Worked example: New construction home is listed at $700,000 plus HST.
- HST: $700,000 × 0.13 = $91,000
- Total before rebate: $700,000 + $91,000 = $791,000
- New Housing Rebate: typically 36% of the federal portion (5%) plus 75% of the Ontario portion (8%) up to a cap. Calculation in 2026 generally yields $24,000 to $30,000 in rebate for homes under $450,000 federal threshold; reduced for homes priced higher.
Resale homes do not generally attract HST. Only new builds and substantially renovated properties do.
8. Land Transfer Tax (LTT)
Ontario charges a marginal tiered Land Transfer Tax. Toronto charges an additional municipal LTT on top.
Ontario LTT brackets (2026):
| Portion of price | Rate |
|---|---|
| Up to $55,000 | 0.5% |
| $55,001 - $250,000 | 1.0% |
| $250,001 - $400,000 | 1.5% |
| $400,001 - $2,000,000 | 2.0% |
| Over $2,000,000 | 2.5% |
Worked example: Sale price $850,000.
- First $55,000 × 0.005 = $275
- Next $195,000 × 0.01 = $1,950
- Next $150,000 × 0.015 = $2,250
- Next $450,000 × 0.02 = $9,000
- Total Ontario LTT: $13,475
If the property is in Toronto, double this amount (Toronto charges its own equivalent LTT on top of the Ontario LTT).
First-time buyers receive a rebate of up to $4,000 in Ontario and up to $4,475 in Toronto.
9. Area Conversions
Old listings sometimes use square feet; some commercial leases use square metres.
Formula:
1 square metre = 10.764 square feet
Worked example: A 1,200 ft² condo.
- 1,200 ÷ 10.764 = 111.5 m²
Acres and hectares appear in rural and commercial contexts:
1 acre = 43,560 ft² = 0.4047 hectares
1 hectare = 2.471 acres = 10,000 m²
10. Mortgage Penalty (IRD vs Three Months' Interest)
When a buyer breaks a fixed-rate mortgage early, the penalty is the greater of:
- Three months' interest, or
- Interest Rate Differential (IRD): the difference between the contract rate and the current rate, multiplied by the remaining principal and time left.
Worked example: $400,000 remaining principal at 5.49%, 24 months left. Current 2-year rate is 4.49%.
- Three months' interest: $400,000 × 0.0549 × (3 ÷ 12) = $5,490
- IRD: $400,000 × (0.0549 − 0.0449) × (24 ÷ 12) = $400,000 × 0.01 × 2 = $8,000
Penalty = greater of the two = $8,000.
How to Practise This Math
Reading the formulas is necessary but insufficient. The exam format requires you to extract numbers from a scenario, identify which formula applies, and compute under time pressure. The path that works:
- Drill 30 to 50 scenario-based math questions per topic rather than abstract formula problems.
- Always show your work, even on practice. When you get a question wrong, you need to know whether you misread the scenario, picked the wrong formula, or made an arithmetic error.
- Use a basic calculator from day one of practice, not your phone. The exam calculator is a basic non-programmable model, and finger-fumbling on exam day is real.
- Review every math question on your wrong-answer queue. Math errors compound: if you got cap rate wrong once, you will likely get it wrong again unless you specifically work through it.
ExamAce's question bank tags every math question by formula type, so you can drill specifically on commission, GDS/TDS, cap rate, etc. without wading through non-math questions.
Calculator Allowed?
Yes. A basic non-programmable calculator is permitted. Bring one. Most students bring a $10 calculator from a drugstore; that is sufficient for everything on the exam. Phone calculators, programmable calculators, and graphing calculators are not allowed and will be confiscated at the proctored exam.
Related on ExamAce
- How to get your Ontario real estate licence
- How hard is the Humber real estate exam?
- What to do if you fail the Humber real estate exam
- Humber real estate Course 4 (Commercial) exam guide
ExamAce is an independent exam preparation platform. Tax rates, mortgage stress-test thresholds, and LTT brackets in this guide reflect 2026 Ontario rules; verify against current government sources before relying on numbers in real transactions.
