Start with the gap between your current rate and what you could get today. A lower rate matters, but it is only part of the math. Closing costs, how long you plan to stay in the home, and whether you roll fees into the new loan all determine when a refinance actually pays off. I'd run a break-even calculation before anything else, because a small rate drop can disappear under fees if you move within a couple of years.
Not every refinance is about the rate. Some homeowners want to move from a 30-year term to a shorter one, drop mortgage insurance, or consolidate higher-interest debt. Others need cash for a renovation or an emergency. Each goal changes the calculation, and a cash-out loan can make sense when it replaces expensive credit card balances. Rates have been moving around quite a bit, so timing matters too, and a rate lock that runs past a major economic announcement adds risk you may not want to carry.
If your current rate sits well below today's market, keeping your loan is usually the right move, and you should be skeptical of any offer that promises to beat it by a sliver. Homeowners who refinanced or bought when rates were higher may see a different picture, especially if their credit has improved or their home value has grown. Equity and home values shift, though, so an appraisal and a current quote should come before any decision. I would rather tell you to stay put than sell you a loan that does not fit.
Keeping your mortgage makes sense when the savings are small or your timeline is short. Refinancing makes sense when the numbers work over the years you plan to stay and the new loan supports a goal you already have.