Projected total interest$131,029
Available credit$450,000
30-Year First-Lien HELOC Calculator
Use your own cash flow to see what the mortgage could do.
Generic payoff claims are not enough. Change the numbers yourself and see how the modeled payoff time, total interest, and available credit respond.
Interactive mortgage comparison
How could a first-lien HELOC change your payoff timeline?
Start with your current or planned mortgage balance, enter an illustrative fixed rate and HELOC rate, then add your monthly take-home income and normal non-mortgage spending.
YOUR CASH-FLOW MODEL
LIVEFirst-lien HELOC vs. a standard 30-year fixed mortgage
Income modeled as$7,500 twice monthly
Monthly cash-flow surplus$6,000
Balance after first deposit$442,500
Approx. HELOC daily interest$83.22 → $81.83
PROJECTED RESULTS
How could this change the payoff timeline?
Positive monthly cash flow is what gives the HELOC model its ability to keep reducing principal.
Projected total interest$600,729
Available credit$0
Modeled difference vs. scheduled 30-year fixed$469,700 less interest
Modeled payoff differenceAbout 21 years 11 months sooner
Your cash flow looks worth modeling with actual lender terms.Change the HELOC rate, income, or spending and the payoff estimate responds immediately.
See model assumptions
HELOC cash flow: Monthly take-home income is modeled as two equal deposits, on the 1st and 15th. Monthly non-mortgage expenses are spread across the month.
HELOC interest: Interest is modeled daily at the constant rate you enter and added monthly. Real first-lien HELOC rates commonly vary and may change.
30-year fixed comparison: The fixed-mortgage baseline uses a standard 30-year amortization and makes only the scheduled principal-and-interest payment. It does not model optional extra principal payments.
Expenses: Exclude your current mortgage principal-and-interest payment from monthly expenses. Include normal household spending and, if appropriate, taxes and insurance paid outside the loan.
Not included: Closing costs, lender fees, future HELOC rate changes, future draws, changing credit limits, or changes in income and spending.
Purpose: Educational illustration only—not a quote, approval, guarantee, or prediction of actual savings or payoff timing.
How to read the result
The most important input is not the mortgage rate. It is the cash flow left after normal life.
The model treats monthly income as two deposits and spreads normal non-mortgage spending across the month. That lets the HELOC balance move down when income arrives and back up as expenses occur.
The long-term payoff is driven by the portion of income that ultimately remains after spending. The daily-balance effect can improve interest efficiency while money remains against the line, but it does not create surplus.
Before you decide
Stress-test the result instead of falling in love with the first number.
If the result still looks compelling, the strategy may be more resilient than a model that only works at one assumed rate.
See how sensitive the payoff is to variable-rate risk before treating the projection as meaningful.
A future child, car payment, tuition bill, or lifestyle change can reduce surplus and move the payoff date later.
Use a conservative number if commissions, bonuses, or business income are inconsistent.