Bio Bay Moon Calendar 2026-2027: find your darkest night.
This bio bay moon calendar rates every night in Puerto Rico by how much moonlight reaches the water during tour hours. The darkest nights run from a few days after the full moon to a few days after the new moon, when the moon is down in the early evening. Enter your trip dates to see your best nights and which of our three bio bay tours run.
How each night is rated
Each night on the bio bay moon calendar gets one of four ratings, based on how much moonlight reaches the water during tour hours, from 45 minutes to 2 hours 45 minutes after sunset. The rating uses where the moon sits in the sky over Puerto Rico and how much of it is lit, so a bright moon that is still below the horizon counts as a dark sky.
- Darkest sky. The moon is down, or no more than a sliver, during tour hours.
- Dark sky. Barely any moonlight reaches the water.
- Some moonlight. The moon is up for part of the evening.
- Moonlit night. A bright moon is up. In Fajardo, our guides use a tarp on brighter nights.
Tap any night to see the moon's phase, how much of it is lit and the time it rises or sets. A white diamond marks the nights the La Parguera tour runs. On this calendar, a typical month has about two weeks of darkest-sky nights and about a week of moonlit nights, with the rest in between.
The calendar's moon phases, sunsets, moonrises and moonsets are checked against U.S. Naval Observatory data.
Best moon phase for a bioluminescent bay
The new moon is the best moon phase for a bioluminescent bay, and the dark stretch around it is longer than most people expect. For evening tours, the sky is darkest from about the fourth night after the full moon, when the moon rises after tour hours, until a few nights after the new moon, when a young crescent sets early.
The moon rises about 50 minutes later each night (EarthSky), so its place in the lunar cycle tells you whether it is up while you are on the water:
- After the full moon, the moon rises a little later each evening, and within a few nights it rises after tour hours.
- Around the new moon, there is no moon in the evening sky. These are the classic darkest nights.
- Just after the new moon, a thin crescent sits low in the west after sunset and sets during the evening.
- From the first quarter to the full moon, the moon is high in the evening sky. These are the moonlit nights.
That is why the phase name alone can mislead. A waning moon that is more than half lit still leaves the lagoon dark when it rises after your tour, and the calendar works that out for every night from moonrise, moonset and how much of the moon is lit.
Can you see the bio bay during a full moon?
Yes, the bio bay still glows during a full moon, but the bright sky makes the blue-green light harder to see. A full moon rises around sunset and stays up through the night, so it is the brightest stretch of the month. If your dates are flexible, the evenings after the full moon get darker each night, and the calendar shows the nearest darkest-sky night.
- Fajardo runs every night. On brighter nights at Laguna Grande, our guides use a large tarp to block the light so your group still sees the glow.
- La Parguera runs on select nights each month, in the stretch after the full moon when the early evening is dark again.
- Vieques is for your nights on the island. Send us the nights you are staying on Vieques and we will confirm the dates for the Mosquito Bay tour.
Great operation and experience! All 4 guides were fun, professional, and experienced. We went on a full moon night, so knew our chances of seeing the bioluminescence was unlikely, but the guides brought a large tarp that went over the entire group, blocking out all the light so we could see the bioluminescence perfectly! Kayaking through the mangroves at night would have been fun enough in its own right, but getting to see the bioluminescence when we weren't expecting to was even better.
Vieques bio bay calendar
The Vieques bio bay calendar below shows only the Mosquito Bay tour. Enter the nights you are staying on Vieques and it picks the darkest ones, rated the same way: moonlight on the water during tour hours, in Puerto Rico time. The tour meets in Esperanza and starts after dark, and there is no same-day ferry back, so it is for nights you sleep on the island.
Picking a dark night early in your stay keeps the rest of your trip open if you would like to go again. The tour is $85 per person in a two-person clear-bottom kayak, ages 3 and up. See the Vieques clear-kayak tour.
Open the Vieques calendar
Darkest nights by month, 2026-2027
These are the darkest-sky nights, new moons and full moons for the next 14 months, worked out for Puerto Rico by the same engine as the calendar. The last column shows the nights the La Parguera tour runs. Every other night also has a rating, from dark sky to moonlit night, on the live calendar.
See all 14 months
| Month | Darkest-sky nights | New moon | Full moon | La Parguera tour nights |
|---|---|---|---|---|
| November 2026 | Nov 1 to 11 and Nov 27 to 30 | Nov 9 | Nov 24 | Nov 28 to 30 |
| December 2026 | Dec 1 to 11 and Dec 26 to 31 | Dec 8 | Dec 23 | Dec 27 to 29 |
| January 2027 | Jan 1 to 10 and Jan 24 to 31 | Jan 7 | Jan 22 | Jan 26 to 28 |
| February 2027 | Feb 1 to 8 and Feb 23 to 28 | Feb 6 | Feb 20 | Feb 24 to 27 |
| March 2027 | Mar 1 to 10 and Mar 25 to 31 | Mar 8 | Mar 22 | Mar 26 to 28 |
| April 2027 | Apr 1 to 8 and Apr 23 to 30 | Apr 6 | Apr 20 | Apr 24 to 27 |
| May 2027 | May 1 to 7 and May 23 to 31 | May 6 | May 20 | May 24 to 27 |
| June 2027 | Jun 1 to 6 and Jun 22 to 30 | Jun 4 | Jun 18 | Jun 22 to 26 |
| July 2027 | Jul 1 to 5 and Jul 22 to 31 | Jul 3 | Jul 18 | Jul 22 to 25 |
| August 2027 | Aug 1 to 4 and Aug 21 to 31 | Aug 31 | Aug 17 | Aug 21 to 23 |
| September 2027 | Sep 1 to 3 and Sep 19 to 30 | Sep 29 | Sep 15 | Sep 19 to 22 |
| October 2027 | Oct 1 to 2 and Oct 18 to 31 | Oct 29 | Oct 15 | Oct 19 to 21 |
| November 2027 | Nov 16 to 30 | Nov 27 | Nov 13 | Nov 17 to 19 |
| December 2027 | Dec 16 to 29 | Dec 27 | Dec 13 | Dec 17 to 19 |
The live calendar at the top of this page is the up-to-date version: it rates every night for the next 24 months and shows moonrise and moonset times.
Which bio bay tours run on which nights
The Laguna Grande kayak tour in Fajardo runs every night, all year, with two evening departures. The La Parguera sunset boat and bio bay tour runs on select nights each month, in the stretch after the full moon. The Mosquito Bay tour on Vieques is for the nights you stay on the island. Tap any night on the calendar to ask for that night.
Not sure which bay suits your trip? Compare the three bio bays, or read the best time of year and time of night to go.
Bio bay moon calendar questions
Is the bio bay glowing tonight?
Yes, Puerto Rico's three bio bays glow year-round, so the glow is there tonight. How well you see it depends mostly on the moon, plus weather and water conditions, and no one can promise a level of brightness. Find tonight's date on the calendar above: it rates tonight's sky during tour hours and shows the next darkest night.
What is the best moon phase to see the bio bay?
The new moon is the best moon phase to see the bio bay, together with the nights around it. For evening tours, the dark run starts about four nights after the full moon, once the moon rises after tour hours, and lasts until a few nights after the new moon, when a young crescent still sets early.
Is a new moon the best night for the bio bay?
A new moon is one of the best nights for the bio bay, but it is not the only one. Many nights before it are just as dark during tour hours, because the waning moon rises after the tour ends. The calendar rates every night, so you can pick the darkest night that fits your trip.
Can you see bioluminescence during a full moon?
Yes, you can see bioluminescence during a full moon, though the bright sky makes the glow harder to see than on a dark night. On brighter nights at Laguna Grande in Fajardo, our guides use a large tarp to block the moonlight. If your dates are flexible, the calendar shows the nearest darker night.
Do bio bay tours run on a full moon?
The Fajardo kayak tour at Laguna Grande runs on full moon nights too, every night of the year, with a tarp on brighter nights. The La Parguera sunset boat and bio bay tour does not run around the full moon: its select nights start in the stretch after it, when the early evening is dark again.
Why does moonrise time matter more than the moon phase?
Moonrise time decides whether the moon is in the sky while you are on the water, and a moon below the horizon adds no light at all. The moon rises about 50 minutes later each night, so a moon that is more than half lit can still leave the bay dark if it rises after your tour.
How many dark nights are there each month?
On this calendar, a typical month has about two weeks of nights rated darkest sky, mostly from a few nights after the full moon until a few nights after the new moon. About a week is rated moonlit night, around the full moon, and the remaining nights fall in between.
What does darkest sky mean on the bio bay moon calendar?
Darkest sky means the moon is below the horizon, or no more than a thin sliver, during tour hours on that night. It is the top of the calendar's four ratings. The other three are dark sky, some moonlight and moonlit night, each with a little more moonlight on the water.
How does this moon calendar rate each night?
Each night is rated by how much moonlight reaches the water during tour hours, from 45 minutes to 2 hours 45 minutes after sunset. The rating uses where the moon sits in the sky over Puerto Rico and how much of it is lit. There are four levels, from darkest sky to moonlit night.
When does the La Parguera bio bay tour run?
The La Parguera sunset boat and bio bay tour runs on select nights each lunar month, in the stretch after the full moon when the sky is dark early in the evening. The calendar marks those nights with a white diamond, and the table of darkest nights by month lists them for the next 14 months.
When is the best night for the Vieques bio bay?
The best night for the Vieques bio bay is the darkest night of your stay on the island. Open the Vieques bio bay calendar on this page, enter the nights you are staying on Vieques, and it picks the darkest ones. Choosing a night early in your stay keeps the rest of your trip open.
Can I enter my trip dates to find my best nights?
Yes, enter your arrival and departure dates at the top of the calendar and it lists the best nights of your trip, rated by moonlight during tour hours. It also shows which nights the La Parguera tour runs. Tap any night to see its moon details and the tours you can book.
Is the bio bay moon calendar in Puerto Rico time?
Yes, every date, sunset, moonrise and moonset on the bio bay moon calendar is in Puerto Rico time, which is Atlantic Standard Time all year with no daylight saving change. If you are planning from another time zone, the night you tap is the night you will be on the water in Puerto Rico.
How far ahead can I check the moon for my trip?
The calendar covers the next 24 months. Moon phases, moonrise and moonset can be worked out years in advance, so the rating for a night next year is as reliable as the rating for tonight. Weather is the part nobody can forecast that far out, so plan the moon now and the weather later.
How do I book a night from the calendar?
Tap a night, then tap Contact Us to Book next to the tour you want. It opens WhatsApp with your tour and date already filled in, and we take it from there. You can also call or text (787) 209-2127. Fajardo tours start at $85 per person.
Found your night?
Send us your dates on WhatsApp and we will help you match the bay and the night to your trip.