Fasting on the day of Arafah (9th Dzul Hijjah) is an expiation for TWO years:

Fasting on the day of Arafah (9th Dzul Hijjah) is an expiation for TWO years:
(“It expiates the sins [Minor] of the past year and the coming year.”)

You should fast and break your fast along with the people of the country where you are living, whether that is in accordance with your country of origin or not. Similarly on the day of ‘Arafah you should follow the country where you are living. (Shaykh Ibn ‘Uthaymeen)

The Messenger of Allah (sal Allahu alaihi wa sallam) was asked about fasting on the Day of Arafa (ninth Dzul Hijjah). He said, “It expiates the sins (minor) of the previous year and of the coming year.” [Book 006, Hadith 2603, Sahih Muslim)

 The above Hadith, as well as other Hadiths of similar nature, refers to minor sins. A person will have to make sincere tawbah for his major sins to be forgiven.

(Refer: Al Minhaj of Imam Nawawi, under Hadith: 2738)

Imaam at-Tirmidhee رحمه الله said,
“The People of Knowledge consider it recommended to fast on the day of ’Arafah, except for those at ’Arafah.”
[Muslim (no. 1348)]