The day that never happens

A tithi is a lunar day. It is not a day of the clock. It is a stage in the growing gap between the moon and the sun, and it ends when that gap has widened by another 12 degrees. Because the moon speeds up and slows down as it goes round, a tithi can be as short as about 20 hours or as long as almost 27.

Indian calendars name each day after whichever tithi is running at sunrise. That works well nearly all the time. But a short tithi can begin after one sunrise and finish before the next. Then no morning ever catches it, so no date gets its name, and somebody reading down the sheet in January 2026 goes looking for the fourth and finds only the third and then the fifth. This is called a kshaya tithi, a lost lunar day.

Nothing has been hidden. A full almanac page shows the fourth sitting inside Tuesday as a second entry, running from 08:01 in the morning until 06:52 the next day. It was recorded to the minute. It just never owned a date.

The missing number is also local. Tithis start and end at the same instant everywhere, but sunrise does not. That fourth lunar day in January 2026 was lost in Delhi and Mumbai, and kept its place in the calendars of Kolkata and Chennai, on the same morning.

So what happens to a fast pinned to a number that is not there? The usual answer is that the observance stays on the earlier of the two days, the one whose name belongs to the previous number, because that is the day the lost tithi actually ran through. That is what happened with Sakat Chauth in January 2026: the fast was kept on a Tuesday that the almanac calls the third.

Traditions do not agree on every case. When the eleventh lunar day is the one that disappears, most calendars keep the fast on the earlier day, while Vaishnava calendars move it to the day after, and both dates are printed on the same page.