Simple Buddhist-Christian Era Calculators
Official Buddhist Calendar
According to the traditional dating the Buddha was born in 624 BC, attained Awakening 35 years later in 589 BC and entered Paribbāna in 544 BC. It is from the latter date that we take the Buddhist Era (Thailand, Cambodia and Laos date it as year 0 or BC 543, Sri Lanka, Myanmar and India as year 1 or BC 544).
Most scholars now think that the actual dates should be set approx. 100 years later (there is much difference in opinion), but the dates in any case should not be taken as hard and fast, but rather as agreed times for the purposes of celebrations, etc. (more details on Wikipedia)
Christian Date
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Buddhist Date
Vikram Samvat
Another calendar that was in use for a long time throughout India is the Vikram Samvat, and it is in use in Nepal to this day. Although this was a Hindu calendar, it was also adopted by Buddhist communities in northern India, and some inscriptions at Buddhist sites use it. The main form of this calendar starts 57 years before the Christian era (more details on Wikipedia)
Christian Date
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Vikram Samvat Date
Cūḷasakarat
Another Buddhist calendar that has been in use in SE Asia is the Cūḷasakarat, whose base date is 638 CE. This is a format that is mainly found in manuscripts and inscriptions over a wide area including Myanmar, Thailand, Laos and Cambodia. (more details on Wikipedia)
Christian Date
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Cūḷasakarat Date