Sankashti Chaturthi is a monthly fast dedicated to Lord Ganesha, observed on the Chaturthi (fourth tithi) of the Krishna Paksha, the waning half of each lunar month. It is one of the few vrats whose date is fixed by moonrise rather than sunrise, so this calendar picks the day whose computed moonrise falls inside the Chaturthi tithi and shows you that moonrise time, which is the moment the fast is broken. No birth details are required - just pick your city.
The name comes from "Sankashti," meaning deliverance from difficult times. The vrat is offered to Ganesha as Vighnaharta, the remover of obstacles, and is believed to bring relief from troubles and the fulfilment of wishes. Because it falls once in every lunar month, there are twelve or thirteen Sankashti Chaturthis in a year.
It is distinct from Vinayaka Chaturthi, which is observed in the bright fortnight (Shukla Paksha). The Sankashti Chaturthi that falls in the month of Magha is regarded as the most important of the year.
Devotees keep a fast from sunrise and break it only at night, after Chandra Darshan - sighting the moon - followed by Ganesha puja with offerings such as modak and durva grass. Since moonrise varies from place to place, both the date and the exact time to break the fast differ by city, which is why this calendar is tied to your chosen location.
Moonrise decides the date as well as the timing, and this is why a Sankashti date can differ from a calendar that simply reads the tithi at sunrise. The Krishna Chaturthi often begins during the daytime and is already running by the time the moon rises that evening, even though the sunrise that morning still fell in Tritiya. On the rare occasion the Chaturthi is short enough to contain no moonrise at all, the fast is kept on the day whose sunrise falls inside it and broken at that night's moonrise; each date on this page states which of the two rules placed it.
The moonrise anchor is not this site's invention, and it is worth naming the sources because they are what makes this calendar differ from a sunrise-tithi listing. Kane, History of Dharmasastra Vol. V Part I, in its list of vratas, cites Dharma Sindhu p. 74, Smrtikaustubha 171 to 177 and Vratarka 180 to 187: Sankashti Chaturthi is the Krishna Chaturthi decided on moonrise, and the fast is broken only after the moon is sighted. Every entry on this page carries the anchor it used and the passage that anchor comes from, so you can check the reasoning rather than take the date on trust.
One popular name here is usage rather than rule, and the calendar says so. When the vrat falls on a Tuesday it is called Angarki, and it is widely held to carry the merit of many months of the observance - but no located text supplies that rule, so the label is shown as a variant name with a note, not as a computed grade. This is the same practice the Pradosh calendar follows with its weekday names.
Both are monthly Ganesha observances tied to the Chaturthi tithi. Sankashti Chaturthi falls in the Krishna Paksha (waning fortnight) and its fast is broken at night after moonrise, while Vinayaka Chaturthi falls in the Shukla Paksha (waxing fortnight) and is centred on midday worship.
When Sankashti Chaturthi falls on a Tuesday (Mangalvar), it is called Angarki Chaturthi. It is considered especially powerful for Ganesha worship, and observing it is believed to carry the merit of many months of the vrat. The name is popular usage rather than a rule from a located text, so this calendar shows it as a variant label with that note attached.
No. Sankashti Chaturthi is a calendar observance, not a birth-chart calculation. Just select your city so the fasting date and the moonrise that ends the fast are computed for your own latitude and longitude.
Because the rite is prescribed for moonrise. Kane, History of Dharmasastra V.i, citing Dharma Sindhu p. 74, Smrtikaustubha 171 to 177 and Vratarka 180 to 187, records that Sankashti Chaturthi is the Krishna Chaturthi decided on moonrise and that the fast is broken only after the moon is sighted. A tithi is selected by the division of the day the rite belongs to, so a sunrise lookup would answer the wrong question here.
Most likely because it reads the tithi at sunrise. The Krishna Chaturthi often begins during the day and is already running when the moon rises that evening, even though that morning's sunrise still fell in Tritiya - so a sunrise-based listing puts the vrat a day later. Moonrise also depends on your latitude and longitude, so two cities can genuinely differ. Each entry here states which rule placed it.
That is rare but possible when the tithi is short. In that case the fast is kept on the day whose sunrise falls inside the Chaturthi and broken at that night's moonrise. The entry says which of the two rules placed the date, so the fallback is visible rather than silent.
For educational purposes. Astrological interpretations are traditional and not a substitute for professional advice.