HomeCalc — Canadian Mortgage & Tax Calculators

HELOC & Second Mortgage Calculator (Canada)

heloc_second_mortgage

Read-only

Compare a HELOC with a second mortgage for tapping home equity in Canada: how much you can borrow (revolving HELOC capped at 65% LTV, total secured borrowing to 80% with an A lender), monthly payments, TDS qualification at the OSFI stress-test rate, and the same for B and private lenders.

Input Schema

Name	Required	Description	Default
`province`	No	Sets the property-tax estimate used in TDS	Ontario
`homeValue`	Yes	Current market value of the home in CAD
`amountToBorrow`	Yes	Amount you want to borrow in CAD
`helocSpreadPct`	No	Lender spread over prime as a percent, e.g. 0.5
`purposeOfFunds`	No	What the money is for	Home Renovation
`helocPrimeRatePct`	No	Prime rate as a percent; defaults to the site's current prime
`existingMonthlyDebts`	No	Other monthly debt payments (car, cards, loans)
`annualHouseholdIncome`	Yes	Gross annual household income in CAD
`extraMonthlyPrincipal`	No	Optional extra principal paid monthly on the HELOC
`secondMortgageRatePct`	No	Second mortgage rate as a percent; defaults to the tier's typical rate
`secondMortgageTermYears`	No	Second mortgage term in years
`outstandingFirstMortgage`	Yes	Balance remaining on the first mortgage in CAD
`secondMortgageAmortYears`	No	Second mortgage amortization in years (not used by interest-only Private)
`secondMortgageLenderTier`	No	A = bank/credit union, B = trust/MIC, Private = individual investor	A

Schema Changelog

Changes observed during successful MCP inspections.

Changed6 schema fields changedNov 2, 2026

removedInput schema / $schema

Removed value: -"https://json-schema.org/draft/2020-12/schema"

addedInput schema / examples

Added value: +[
+  {
+    "amountToBorrow": 100000,
+    "annualHouseholdIncome": 160000,
+    "homeValue": 900000,
+    "outstandingFirstMortgage": 450000
+  }
+]

addedInput schema / properties / province / description

Added value: +"Sets the property-tax estimate used in TDS"

addedInput schema / properties / purposeOfFunds / description
```
Added value: +"What the money is for"
```

addedInput schema / properties / secondMortgageAmortYears / description

Added value: +"Second mortgage amortization in years (not used by interest-only Private)"

addedInput schema / properties / secondMortgageTermYears / description
```
Added value: +"Second mortgage term in years"
```

First observedOct 15, 2026

TDQS

A3.7/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already establish readOnly, non-destructive, closed-world, so the safety profile is covered. The description adds genuine domain behaviour an agent could not infer: the revolving HELOC is capped at 65% LTV, total secured borrowing at 80% with an A lender, and TDS is assessed at the OSFI stress-test rate, with separate treatment for B and private lenders. It does not disclose how defaults (prime rate, tier rates) are resolved or what the response contains.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

A single sentence with the comparison verb front-loaded and no filler. It is dense and slightly run-on in the final clause ('and the same for B and private lenders'), but every clause carries real information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 14-parameter calculator with no output schema, the description covers the computational model and enumerates what the result contains (borrowing capacity, monthly payments, TDS qualification, per-lender-tier results). What is missing is how optional defaults are applied and the shape of the returned comparison, which matters given the absence of an output schema.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% across 14 parameters, so the schema already carries enum meanings, units, defaults and ranges. The description adds framing by tying the inputs to the 65%/80% LTV and OSFI stress-test logic, but does not explain specific parameters such as helocSpreadPct or secondMortgageLenderTier beyond what the schema states. Baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

Specific verb and resource: 'Compare a HELOC with a second mortgage for tapping home equity in Canada', with the exact outputs named (borrowing limit, monthly payments, TDS qualification). It does not name a sibling, so an agent must infer that mortgage_affordability and mortgage_payment are different tools, but the HELOC/second-mortgage framing is narrow enough to be unambiguous.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is only implied by the described computation – the agent can infer this is the tool for equity-tapping comparisons rather than a plain mortgage payment or affordability calculation. There is no explicit 'use this when…' statement, no prerequisites, and no exclusions relative to mortgage_affordability or mortgage_payment.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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