The almanac
The Moon Calendar
The moon phase matters more than the season for seeing bioluminescence. The best nights fall within three days of a new moon, when the sky is darkest. A full moon can wash out the glow almost completely, in any bay, any month.
Check your dates
Are your nights any good?
Enter the nights you will be in Puerto Rico. This checks them against the new moon, the full moon, and the Mosquito Bay closure.
One hard rule, Vieques only
Puerto Rico's Department of Natural and Environmental Resources (DRNA) does not allow any company to run Mosquito Bay tours on the night before, the night of, or the night after a full moon. Those three nights each month are not a poor view, they are a closed bay, and there is no tour to book. Permitted Vieques operators state the same rule on their own sites: Abe's Snorkeling, one of the eighteen operators listed here, publishes it as DRNA regulation (opens in a new tab). Laguna Grande and La Parguera do not have the closure, and some Fajardo operators sell a full-moon kayak tour specifically, though the glow is much weaker then.
October
Anno MMXXVI · 2026
New moon and the three nights on either side, when the glow is strongest. Struck dates mark the full moon, when it is weakest.
November
Anno MMXXVI · 2026
New moon and the three nights on either side, when the glow is strongest. Struck dates mark the full moon, when it is weakest.
December
Anno MMXXVI · 2026
New moon and the three nights on either side, when the glow is strongest. Struck dates mark the full moon, when it is weakest.
January
Anno MMXXVII · 2027
New moon and the three nights on either side, when the glow is strongest. Struck dates mark the full moon, when it is weakest.
February
Anno MMXXVII · 2027
New moon and the three nights on either side, when the glow is strongest. Struck dates mark the full moon, when it is weakest.
March
Anno MMXXVII · 2027
New moon and the three nights on either side, when the glow is strongest. Struck dates mark the full moon, when it is weakest.
What it costs to get there
The cheapest month is rarely the darkest one
Fares below are the lowest recently seen to San Juan from eleven mainland airports, with each month's new moon printed next to it. Read your own airport and ignore the rest.
Flying from New York
Oct 2026
New moon 10th$262
Nov 2026
New moon 9th$232
Cheapest month shown from New YorkDec 2026
New moon 9th$271
NonstopJan 2027
New moon 7th$391
Flying from Miami
Oct 2026
New moon 10th$84
NonstopCheapest month shown from MiamiNov 2026
New moon 9th$103
NonstopDec 2026
New moon 9th$208
NonstopJan 2027
New moon 7th$310
Nonstop
Flying from Orlando
Oct 2026
New moon 10th$145
NonstopNov 2026
New moon 9th$134
Cheapest month shown from OrlandoDec 2026
New moon 9th$148
NonstopJan 2027
New moon 7th$167
Flying from Philadelphia
Oct 2026
New moon 10th$163
NonstopNov 2026
New moon 9th$146
Cheapest month shown from PhiladelphiaDec 2026
New moon 9th$198
NonstopJan 2027
New moon 7th$295
Nonstop
Flying from Atlanta
Oct 2026
New moon 10thNo cached fare for this month.
Nov 2026
New moon 9th$174
Cheapest month shown from AtlantaDec 2026
New moon 9th$233
NonstopJan 2027
New moon 7th$219
Flying from Boston
Oct 2026
New moon 10th$414
Nov 2026
New moon 9th$360
Dec 2026
New moon 9th$372
Jan 2027
New moon 7th$275
Cheapest month shown from Boston
Flying from Chicago
Oct 2026
New moon 10thNo cached fare for this month.
Nov 2026
New moon 9th$261
Dec 2026
New moon 9th$196
Cheapest month shown from ChicagoJan 2027
New moon 7th$215
Flying from Dallas
Oct 2026
New moon 10thNo cached fare for this month.
Nov 2026
New moon 9thNo cached fare for this month.
Dec 2026
New moon 9thNo cached fare for this month.
Jan 2027
New moon 7th$318
Cheapest month shown from Dallas
Flying from Houston
Oct 2026
New moon 10thNo cached fare for this month.
Nov 2026
New moon 9thNo cached fare for this month.
Dec 2026
New moon 9th$587
Jan 2027
New moon 7th$292
Cheapest month shown from Houston
Flying from Charlotte
Oct 2026
New moon 10th$237
Cheapest month shown from CharlotteNov 2026
New moon 9th$367
Dec 2026
New moon 9th$354
Jan 2027
New moon 7thNo cached fare for this month.
Flying from Washington DC
Oct 2026
New moon 10th$254
Nov 2026
New moon 9th$194
Dec 2026
New moon 9thNo cached fare for this month.
Jan 2027
New moon 7th$163
Cheapest month shown from Washington DC
Cheapest round trip found on October 19, 2026, in US dollars, for each departure month. These are the lowest fares recently seen by a fare-tracking service, not live quotes and not an offer. Treat them as a guide to which months run cheap, and check a real booking site for what you can actually buy today. A dash means no recent fare was cached for that route and month, not that no flights exist.
Ready to price a specific week? Search live fares on Aviasales. We earn a small commission if you book through that link, at no extra cost to you. See our affiliate disclosure.
For why late summer is cheap and what that tradeoff costs you, read when to fly for a bio bay trip.
Then pick a bay
A date is half the decision
The moon phase sets the night. The bay sets everything else: how far you travel, whether you paddle or ride, and whether you can get in the water at all.
The brightest bioluminescent bay in the world, and the one bay with a hard rule: DRNA closes it for the three nights around every full moon, so the calendar above decides whether there is a tour to book at all.
The closest bio bay to San Juan, about 45 minutes by car, by kayak or electric boat. No full-moon closure, so a weaker glow on a bright night is still a trip you can take.
The only one of the three where swimming is allowed. Boat tours as well as kayaks, and no closure around the full moon.
Still deciding, or want to compare all three side by side? Read which bio bay you should visit, or go straight to all 17 bioluminescent bay tour operators.
Where to stay near the bays
Most visitors keep San Juan as a base and drive out for the tour: Laguna Grande is about 45 minutes away, and the Vieques and La Parguera trips start from here too. This map shows places to stay in San Juan. Each bay page has its own map if you would rather sleep closer to the water.
Bioluminescent dinoflagellates glow when disturbed, and that glow is genuinely faint. Any light pollution, moonlight included, drowns it out. A new moon gives the darkest sky, which is why the window above is built around it, not around the season or the weather forecast.
Once you have two or three candidate weeks, price those months against the fares before you commit.