Why This Tool Exists
People argue about which is cheaper. The real question is which is less fragile when reality happens: timeline slips, rates change, or cash flow tightens.
This calculator helps you compare the cash flow and the hidden cost (opportunity cost) so you can pick the tool that matches your risk tolerance.
Loan Comparator (HELOC vs 401k Loan)
Compare payment, interest cost, and opportunity cost using conservative assumptions.
| Scenario | HELOC rate | HELOC interest | Opp. cost | Quick read |
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What To Model (So You Do Not Fool Yourself)
The payment you can actually afford matters more than the interest rate you prefer.
Opportunity cost is the hidden lever on retirement-account loans. If markets go up while your money is out, that is a cost.
For HELOCs, rate risk is the hidden lever. Model a higher rate scenario to stress test.
Execution Notes
Pick a conservative expected return for opportunity cost. Optimism is how you rationalize bad leverage.
If you are using leverage for a down payment, pair it with a written downside plan and liquidity reserves.
Keep your documentation clean. Lenders and advisors care about the paper trail.
Documentation Checklist (Keep It Defensible)
- Create a one-page objective memo before you execute (what outcome you are trying to buy).
- Store your assumptions and calculations in a dated PDF (no year-end reconstructions).
- Keep evidence in the same folder structure every month (receipts, logs, approvals).
- Ask your CPA what would make this easy to sign off on, then build that packet.