From Longman Dictionary of Contemporary Englishbe in luckbe in luckLUCKYto be able to do or get something, especially when you did not expect to You’re in luck – it’s stopped snowing. → luck
Examples from the Corpus
be in luck• You're in luck, there are still a few tickets left.• You're in luck. There's one ticket left.• If you like Californian wine you could be in luck - we are giving away 100 bottles of Cabernet Sauvignon.• If you are partial to Californian wine, you could be in luck.• He was in luck because a cab drew up alongside him and a man got out.• But here too Mr Kohl is in luck.• The problem is that it went too far and now I think they might be in luck.• If not, the hyenas would soon be in luck once more.• Round another bend - and we were in luck.• And you are in luck, pretty lady. 