Compare both loans at the same sale date
Start with the month you expect to sell. Estimate what you would pay from now until then if you keep the existing loan and if you refinance. Include upfront loan charges after credits, principal-and-interest payments, and the estimated loan payoff at sale under each option. If you roll charges into the loan, account for them through the new balance and payments. Keep taxes, insurance, and escrow funding separate so timing differences do not look like loan savings.
Worked example
If a refinance costs $4,800 upfront and cuts principal and interest by $200 a month, the simple payment break-even is 24 months. A sale at month 12 captures $2,400 in payment savings, leaving $2,400 of the upfront charge unrecovered on that measure. At month 30, payment savings exceed the upfront charge by $1,200. The full comparison can differ if the two loans have different payoff balances at sale.
Run the numbers at your expected sale date and at an earlier or later date you could realistically face. Ask for written terms and disclose your sale plans if the property is listed or you expect to list it soon. Verify any payoff charges before relying on the comparison.
See the refinance holding-period example and the guide to comparing refinance costs.