Answered by: Maulana Muhammad Asadullah Anwar Adam
Is it haram to fast on Thursday, yet Friday is Ramadan?
In the name of Allah, the Most Gracious, the Most Merciful
The Prophet (ﷺ) said, “None of you should fast a day or two before the month of Ramadan unless he has the habit of fasting (Nawafil) then he can fast that day.” 
A person should not fast a day or two before Ramadan unless that day lines up with a day he would’ve fasted anyways. So if a person fasts every Thursday then he can fast the Thursday before Ramadan starts on Friday.
 Sahih al Bukhari 1914]
Only Allah knows best
Written by Maulana Muhammad Asadullah Anwar Adam
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham