HELOC Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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HELOC Calculator turns the values on the form into a focused planning estimate. It estimates available HELOC capacity from home value, mortgage balance, and a maximum combined loan-to-value, and also estimates interest-only cost on the planned draw and keeps the arithmetic visible enough to sanity-check.

What this calculator does

HELOC Calculator estimates available HELOC capacity from home value, mortgage balance, and a maximum combined loan-to-value, and also estimates interest-only cost on the planned draw. The form asks for home value, current mortgage balance, max combined loan-to-value, heloc annual rate, planned heloc draw, and interest-only draw period. The result should therefore be read as a calculation from those displayed assumptions, not as live market, lender, tax, or government-program data unless the page explicitly supplies such a feed.

How to use it

Enter Home value, Current mortgage balance, Max combined loan-to-value, HELOC annual rate, Planned HELOC draw, and Interest-only draw period. Keep monetary inputs in one currency; the currency selector formats results and does not convert exchange rates. Enter rates and percentages on the scale shown by the field label; do not silently switch between a decimal and a percent. Keep time values in the period shown on the form so a monthly figure is not accidentally entered as an annual one or vice versa. Before calculating, recheck Home value, Current mortgage balance, Max combined loan-to-value against the source values you intend to model. If a default value is already filled in, confirm that it matches the scenario you actually want to test rather than assuming the preset is current or personally appropriate.

How the calculation works

Maximum HELOC capacity = home value × max CLTV − current mortgage balance. Interest-only payment on the planned draw = draw amount × annual HELOC rate ÷ 12. This is the calculation method to use when checking the result from HELOC Calculator; values not represented by a visible input should not be inferred as part of the model.

Example

A $450,000 home at an 85% max CLTV allows $382,500 of combined liens. Subtracting a $300,000 mortgage leaves $82,500 of modeled HELOC capacity. A $50,000 planned draw at 9% is about $375 of interest-only cost for one month.

How to interpret the result

The capacity result is the modeled room under the entered CLTV ceiling. The planned-draw interest figure shows interest-only cost at the entered rate, not a full repayment-phase payment. Keep the assumptions with the result so a later recalculation can be compared consistently.

Limitations and notes

HELOC approval depends on appraisal, credit, income, lender CLTV limits, minimum draw, fees, variable-rate index and margin, and underwriting. Rates can change, and the repayment period can require principal payments. Rounding and timing conventions can cause a real statement or account balance to differ slightly from the model.