Mathematicians and geometricians around the world celebrate “Pi Day” on March 14 (3/14, get it?). The day was actually made a national holiday in the U.S. back in 2009, so it’s official. To celebrate this year, United Airlines is launching a one-day fare sale with one-way ticket prices starting at $31.40 or 3,140 miles (plus taxes and fees starting at $5.60). These fares will only be available as long as seats last, and until tomorrow, March 15, at the latest.
So if you have some upcoming travel plans, this could be a good way to save some money on them.
United has set up a special sale page where you can book these tickets. They are valid for travel dates from March 28 – June 5, 2021. The tickets being sold are in United’s barebones Basic Economy fare class, so the restrictions include no seat selection, no group or family seating, no full-sized carry-on bags, and no flight changes or refunds except during the first 24 hours after purchase. That said, you can usually purchase seat assignments in advance.
You will also only find this pricing available for travel on Monday, Tuesday, Wednesday, and Thursday, so unfortunately the weekends are ruled out. Given how short many of the routes on sale are, most seem tailor-made for quick getaways, and these constraints might not be so onerous. Also keep in mind that the seats available for these special prices are capacity controlled and might not be available on all flights or dates that fall under the promotional period.
The full list of city pairs between which these fares are available can be found on the sale page. Most are either from the airline’s hubs, or on short, heavily trafficked route. Here are a few examples:
Boston (BOS) – Newark (EWR)
Boston (BOS) – Washington, D.C. (IAD)
Chicago (ORD) – Detroit (DTW)
Chicago (ORD) – St. Louis (STL)
Denver (DEN) – Salt Lake City (SLC)
Denver (DEN) – Houston (IAH)
Houston (IAD) – Tulsa (TUL)
Houston (IAH) – New Orleans (MSY)
Los Angeles (LAX) – San Francisco (SFO)
Los Angeles (LAX) – Phoenix (PHX)
Newark (EWR) – Cleveland (CLE)
Newark (EWR) – Portland, Maine (PWM)
Washington, D.C. (IAD) – Greenville (GSP)
Washington, D.C. (IAD) – Providence (PVD)
Those are just a few examples. There are currently over 70 city pairs listed among the eligible routes. Even if you cannot take advantage of one of those, though, there are hundreds of other routes on sale for prices ranging between $49 and $139, or and 5,500 to 12,500 miles (though at these higher levels, your per-mile value goes down). At the pricier end of the spectrum are longer-haul domestic itineraries, such as Boston to Los Angeles and San Francisco, Denver to Miami, and Chicago to Seattle.
United is offering a clever promotion tied to Pi Day that math geeks and humanities majors alike can take advantage of. While none of the sale fares is earth-shattering, and purchasing one means you will be stuck flying in Basic Economy with all the limitations that entails, if you do have some upcoming travel and some of these routes suit your needs, you might as well save cash or miles booking tickets. Just remember to do so by tomorrow, March 15, in order to enjoy the preferential pricing before the sale period ends.
This article originally appeared on Forbes