Answered by Ustadh Tabraze Azam
Question: Assalam alaykum,
A Muslim, ignorant of the importance of fasting in Ramadan, did not fast nor make the intention to fast for many years. After repenting, he calculated he had missed about 400 fasts in his life. Does he have to make up the 400 fasts? Is an expiation (Kafara) necessary?
Answer: Assalam alaykum wa rahmat Allah,
The person would need to make up the missed fasts and repent for his mistake. However, an expiation would not be due in such a case because expiation is only due upon fasting persons who commit major contraventions without excuse.
Please see: A Reader on Tawba (Repentance)
And Allah alone knows best.
Checked and Approved by Shaykh Faraz Rabbani