Whether you’re buying a home or refinancing, there’s a moment you’ll have to choose whether to pay points or not.

Today there’s a new wrinkle. Is the extra expense of points worth it when interest rates are already at stunning lows?

In fact, paying points can be more profitable when rates are low — but only marginally so. It takes years for an investment in points to be profitable, so this option should be weighted against alternative uses for the money.

Points are upfront interest charges that go to the lender the moment the deal is closed. Each point equals 1% of the loan amount. One point would cost you $1,000 for every $100,000 borrowed. Freddie Mac (Stock Quote: FRE), the government-backed mortgage company, says the average 30-year fixed-rate mortgage charges 4.49% and 0.7 points.

If you pay points, you get a slightly lower mortgage rate — historically each point reduces the loan rate by 0.125 to 0.250 percentage points. The lower rate reduces your monthly payment. You come out ahead if you have the loan long enough for that savings to exceed the cost of the points. The Mortgage Points Calculator can guide you through the math.

The calculator figures your total costs over a given period with two alternatives — paying points and getting a lower rate, not paying points and using that cash for a bigger down payment, which reduces the loan amount and monthly payment.The calculator’s default figures show the effect of paying two points to cut the loan rate from 6.5% to 6% on a $200,000 loan. After 10 years, paying points would have saved the borrower $4,770 in monthly payments. But the borrower’s loan balance would be $1,210 higher because it started at $200,000 instead of $196,000. So the borrower’s total savings would be $3,560.

Let’s look at the same loan using current interest rates. The mortgage search tool shows it’s fairly easy to find a 30-year fixed-rate loan at 4.75% with no points or 4.25% with about two points.