When is Passover?
"On the fourteenth day of the first month at twilight is the LORD'S Passover" (Leviticus 23:5).
While the answer is straight forward, mapping this day to our calendar is more challenging because Israel used lunar months. As a result, most years had 12 months but periodically they had a leap-month to keep the calendar roughly aligned to the solar year.
The first month of the year roughly occurred at the spring equinox. Hence, the year started about mid-March by our calendars. The fourteenth day of the month would place it near the end of March or during the early days of April, depending on when the next leap-month would be coming.