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To prevent further confusion, in the UK it's known as Mothering Sunday, and this year it's 15 March, 2015. https://en.wikipedia.org/wiki/Mothering_Sunday

I'd say it's more commonly referred to as "Mothers Day" in the UK than "Mothering Sunday". Maybe it depends on whereabouts you're from.

A comic to go with the explanation http://satwcomic.com/mother-s-day