Asalaamu alaikum Mufti saheb,
I have some fasts that I must make up from when I was younger. The fasts that I must make up were from several different Ramadhans. Since a lot of time has passed, I can not remember how many fasts from each particular Ramadan I missed. The best I can do is make a rough estimate of how many fasts I have to make up in total.
Is it okay therefore when making my intention for the Qadha fast to simply say I am fasting to make up the first fast that I missed. Or must I specify the year?
In the name of Allāh, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-raḥmatullāhi wa-barakātuh.
It is not necessary for a person who has Qadha (missed) fast to remember the exact date when making up for the Qadha. Ulama suggest that if a person has several years of Qadha Fast and he does not remember the number of Fast he missed, then he should adopt the following method in completing his missed Fast:
It will suffice for a person to merely say in his intention that this is a Qadha of the first (or last) Fast he missed. He should continue with this intention until he has total conviction that he has fulfilled all his Qadha fasts.
And Allah Ta‘ala knows best
Mufti Luqman Hansrot
 وإذا كثرت الفوائت يحتاج لتعيين كل صلاة فإن أراد تسهيل الأمر عليه نوى أول ظهر عليه أو آخره وكذا الصوم من رمضان.
(نور الإيضاح – ص100 )