Countdown
A live countdown to Mother's Day, calculated from the actual rule — the 2nd Sunday of May in the US and most countries that observe it on this date.
The US, Australia, Canada, and most other countries that observe a "Mother's Day" use the 2nd Sunday of May, calculated live above — but the UK observes "Mothering Sunday" instead, tied to the Christian calendar (the fourth Sunday of Lent, three weeks before Easter), which usually falls in March, weeks earlier than the US date. A handful of other countries use entirely different fixed dates tied to their own history.
The modern US observance traces to Anna Jarvis's campaign in the early 1900s, officially recognized by US federal proclamation in 1914 — deliberately set on a Sunday from the start, which is why the "2nd Sunday" rule has remained the definition ever since rather than a fixed calendar date.
Related
The equivalent US countdown, 3rd Sunday of June.
The exact logic behind this date, for any similar rule.
A countdown to any other custom date.