What do you mean by Free Will?
Calvinists deny the western idea of free will which claims that man is unbiased and neutrally makes decisions.
Calvinists believe that humans are not neutral but biased. We have a sin nature, therefore we can only choose within the spectrum of evil.
as it is written:
“None is righteous, no, not one;
All have turned aside; together they have become worthless;
no one does good,
not even one.”
The LORD saw that the wickedness of man was great in the earth, and that EVERY intention of the thoughts of his heart was ONLY EVIL continually.
So, under that definition we agree that both predestination and free will are true.
We also agree that God predestined a person’s free choices. God has determined how much sin & which sin he will allow us to do. He will allow people to do terrible things to accomplish his own purposes to his glory, this is sometimes referred to as “harden the heart” (Exodus 9:12) & all of this was planned in eternity past.
The heart of man plans his way, but the LORD establishes his steps
As for you, you meant evil against me, but God meant it for good, to bring it about that many people should be kept alive, as they are today.
Evil is terrible & God hates it, but it’s existence is used for good “And we know that for those who love God all things work together for good, for those who are called according to his purpose.” Romans 8:28
Remember that Calvinism does not affirm determinism, the idea that we do things because God made us do things. We’re obviously to the contrary.