Start with cash flow
Cash-flow savings compare the payments you would make on each loan and subtract upfront refinancing fees. This is useful for understanding monthly breathing room. When fees are financed, the upfront bill is smaller but the new starting debt is larger.
Add the balance difference
At your chosen horizon, add the old remaining balance to the cash-flow savings and subtract the new remaining balance. This adjusts for principal that has merely been postponed. If a refinance saves $8,000 in cash payments but leaves $11,000 more debt, the balance-adjusted result is $3,000 worse before excluded effects.
A first crossing is not a permanent win
The calculator reports the first month each measure becomes favorable. Later cash flows can change the result, especially when the original loan ends first. Inspect the result at the time you expect to sell or refinance and also check the full-life interest-and-fee difference.
Know what to add outside the model
This comparison excludes mortgage-insurance changes, cash-out proceeds, taxes, investment returns and escrow adjustments. Use it to understand loan mechanics, then reconcile those other items with actual lender disclosures before making a decision.
Educational information, not personalized advice. See the model assumptions and limitations.