Do Human Beings have a Free Will or their Destinies are Predetermined?

Actually it's both...
As a muslim what I believe is, Allah SWT is already aware of our actions, what we are gonna do in our life, what we gonna gain, how much respect we gonna have in this life etc

Surah Al-Hadid (The Chapter of Iron) verse 22 states:
“No calamity befalls on the earth or in yourselves but it is inscribed in the Book of Decrees (Al Lawh Al Mahfooz) before We bring it into existence. Verily, that is easy for Allah.”

But that doesn't mean that human beings dun have choice or free will, That's the reason Allah has given us "wisdom" or "the power of think" We think and make efforts to wards it but it's Allah's will if it does happen or not.For example, I wanted to go somewhere for study, I choose one thing and I made efforts too but that doesn't happen, Bcoz it want destined for me by Allah. Today, Im doing something else but I'm satisfied. It also says that dua can change qadar/taqdeer so its not hard rule that whatever has been written will happen except for few things.

Source: http://islamiclearningmaterials.com/fate-and-destiny-in-islam/

I believe in the major things being written in Taqdeer/Destiny such as death. Other than that I believe we have freewill through which we can change our own destiny.
In this video (http://www.youtube.com/watch?v=95lh2Dtt4eA) Zakir Naik says that we don't make decisions because its written in Taqdeer, but instead Allah wrote it in Taqdeer because we would make this choice meaning that we have the freewill to make our own decisions.

Now answering Ali Iqbal's question that if God doesn't know our decisions (hence ensuring our freewill), this would be a limitation on God. A question like this had been in my mind ever since I was a kid ;) But here's what I think now: If Allah has written our decisions from "before", we cannot possibly have freewill. But the thing here is, what is "before" outside of the concept of time? The time dimension started existing when this universe began and outside of this context perhaps there is no such thing as time. So if you look at it that way, we humans are unable to understand how that would work. Perhaps there is a way to have "written" our destinies and still give us freewill? Our knowledge is limited, Allah knows best :)

In All of the above comments no one mentioned his thoughts while keeping religion aside so bare with me when I do ;)

Rationally thinking the predetermined fate is so a BS.. If everything was predetermined than it gives you an excuse to not even think for yourself and blame your failures on your fate and the list goes on..

IMO free will exist and every decision that a person makes will effect everything around him.
People in support of fate usually say that they did everything and still the results were not as they expected so it was fate but the simple answer to that is that there are so many random variables in your environment that you can never control all of them according to your wish, resulting in an outcome which you were not expecting.

Now lets take this to a philosophical level.
As Usama said about major events being written in your fate/taqdeer like death. That may or may not be true. Without taking hints from one's religion no one can be sure about this. There is just no way that you would know if certain event was fate or outcome of series of free willed actions.

If there is a higher power than us (i.e. God) and if He is as omnipotent as we think He is.. then it is logical to assume that He would not be bound by time (as we understand it) and as a result we may have free will in all our actions but at the same time He knows what our actions will be because He can see past, present and future at the same time.

From the life lessons, I have learned that whatever happens, happens for the good. We might not find that good immediately but at some point in life, we will understand that the decision (which was made contrary to what we wanted) was actually good for us.
So, although sometimes we do actions and make decisions and think that we have free will, but they are actually pre defined. Like, they are already written and some of us do not want to accept it. But then, you might think what is the use of praying, when everything is already written. Well, I believe, may be its written this way, that we are going to pray and those prayers are going to get accepted (or may be not immediately). We have limited knowledge. We do not even use 2% of our brain throughout over lives and how can we decide if its fate or free will?
We cannot deny the fact that everything is pre planned and it is our destiny, but on the other hand we cannot leave our free will as well.

Al-Qur’an
Information-1
???????? ????? ?????? ?????????? ???????????.
Simple translation: And He has created everything and determined his Taqdir.
(Forqan: 2)
Information-2
?????????? ??????? ???????.
Simple translation: He has determined Qadr (Taqdir) and then He has shown the
way. (Al Ala: 3)
Information-3
?????? ????? ?????? ??????????? ????????.
Simple translation: I have created everything with Qadr (Taqdir).
(Qamar: 49)
Information-4
????? ????? ??????? ???????? , ???? ?????? ????? ??????? ????? ??????? .
Simple translation: Allah never stops before completing His work. Allah has
determined Qadr (Taqdir) of all things. (Talaq: 3)
Information-5
???????? ????????? ???????? ??? ???????.
Simple translation: And He distributes Rijik (livelihood) according to Qadr (Taqdir) as
determined by Him. (Shura: 27)
------------------------------------------------------
Al-Hadith
Information-1
???? ?????? ????? ???? ?????? ????? ???????? ??????? ????? ?????? ????? ???????? ????????? ??????? ??????
????? ?????????? ???????????? ?????? ???? ???????? ????????????? ??????????? ??????????? ?????? ?????? ?????
??????? ???????? ????? ????????. (???? ????)
Simple translation: Abdullah Bin Amar (R) has said, the prophet says, Allah has
written down the Taqdir of His all creations five thousand years before the creation of
skies and earth. At that time Allah’s Arsh (Throne) was above the water.
(Muslim)
Information-2
???? ????????? ???? ?????????? ????? ????? ???????? ????? (?) : ????? ??????? ??? ?????? ????? ??????????
??????? ???? ???????? ? ????? : ???????????? ?????: ???????? ?????????? ???????? ??? ????? ????? ???? ???????
????? ?????????. ???? ??????? ???? ???? ????? ????? ????????.
Simple translation: Hazrat Ubaida Bin Samet (R ) has said, the prophet says, Allah
first made a pen. Then He ordered the pen to write. The pen asked what to write?
Allah said write ‘Qadar’ (Taqdir). So the pen wrote what were present and what will
continue to happen for infinite time.
(Tirmizi narrated the Hadith and termed it ‘Garib’)
Information-3
?????? ?????? ?????? ????? ????? ???????? ????? (?) ????? ?????? ???????? ?????? ????????? ???????????? .
???? ????.
Simple translation: Ibn Omar (R) said, the prophet says, everything has been created
with Qadar (Taqdir), even the sharpening or weakening of intellect.
(Muslim)
Information-4
?????? ?????? ????????? ???? ???????? ????? ??????: ??? ???????? ?????! ?????????? ?????? ???????????????
????????? ?????????? ???? ????????? ???????????? ???? ??????? ???? ?????? ????? ???????? ?????: ???? ???? ?????? ?????.
???? ???? ???????? ???? ????.
Simple translation: Hazrat Abu Khojama has narrated from his father. One day I
asked the prophet (SM): O Messenger of Allah, can the supplications that we read,
the medicine with which we treat or the different ways by which we try to protect us,
resist Taqdir at all? The prophet said your all those efforts are also included in
Taqdir. (Ahmad,Tirmizi, Ibn Maza)
Information-5
???? ????? ?????????? ????? ????? ??????? ????? ?????? ????? ???????? ????????? ??? ???????? ??????????? ???????
????????? ?????????????? ??????????? ???????????? ??????? ????? ??? ??????? ?????.???? ???????
Simple translation: Abu Huraira (R) has said, the prophet says, no woman should
want Talaq of her sister (other woman) to get herself married. Because, she will get
what has been determined by her Taqdir.

For me, it's more like we have free will but its consequences have been most likely paved. Like say, we have two roads... what we see ahead, regardless of what we choose... has already been there even before we arrived. And Allaah knows best.

As Muslims we do believe in fate but that does not mean fate is absolute, so my take on this is that we are expected to work hard for the results that we want and should then leave the rest to Allah and believe in the destiny.

I honestly don't believe in pre-written destiny. Being a Muslim, I know that the one with good deeds will enter Jannah vice versa but its also in Quran that the actions you take can change your fate. So at our level, we can never know about our destiny. This is why I feel like we should think of all the options and do whatever we feel is right. That way we took responsibility of our actions and don't end up cursing our destiny.

i Have free will, dunno about it being Predetermined, and i dont care if it is... as long as i dont know about it :P

Well you'll be shocked to know that I don't have a itsy bitsy beleive in predetermined destiny.... We only get what we strive for, work hard and u'll get whatever you want... and when we don't get something we blame not ourselves buh destiny for that...
" Destiny is for losers... It's just a stupid excuse to wait for things to happen instead of making them happen... "
=)

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Source: https://innnews.pk/human-brain-like-a-10-million-processor-supercomputer-started-working/