Is it considered a sin to not pay Zakat for past years and how can we calculate it?

“My father and for some time my self have not paid Zakat , alhamdullilaha now I am paying ,is it necessary to pay Zakat of yeas for which we have not paid? How to calculate it as there is wast difference in eaRubbing itter(Perfume) to beard is sunnah? What is Sunnah of applying itter (Perfume) rning that time and now”