You've heard the rule: "Refi if your new rate is 0.75% below your current rate." It's been quoted in personal-finance columns for thirty years. It was already a bad heuristic in 1995. It's worse now.
The problem with the 0.75% rule is that it ignores the only two numbers that actually matter: how much your closing costs are, and how long you'll be in the home before you sell or refi again.
A 1.5% rate drop on a $200K loan saves you maybe $180/month. If your closing costs are $8K, you need 44 months to break even. If you're planning to move in 3 years, you've just paid $8K to save $6,500. That's a loss, even though the rate drop "passed" the 0.75% rule.
The opposite case is also true. A 0.5% rate drop with $1,500 in closing costs can pay back in 8 months. If you're staying long enough, that's an obvious refi — even though the rate drop "fails" the 0.75% rule.
Real test: closing costs ÷ monthly savings < months until you'll move or refi
That's it. That's the entire decision. The calculator above runs this math for your specific file. If the break-even is shorter than your ownership horizon, refi. If not, don't.