"I actually will" is correct and usable in written English.
You could use it to stress that you will do something, for example: "I was considering not going, but I actually will."
Perhaps if I put it right beside the bed then I actually will.
So all these people that threaten to leave the country and then don't – I actually will leave that country".
"I became convinced that it was important for the families to know that I actually will take the time and that I care," he said.
"You know I actually will probably read this when I am in the Oval Office when I am deeply frustrated and I am sure it will give me strength and calm me down," said the president, smiling broadly.
"I actually will probably read this when I'm in the Oval Office, when I am deeply frustrated, and I am sure it will give me strength," Mr Obama said.
"Little did I realize that I actually will be".
Which I actually believe will happen, eventually.
It almost motivates me to want to get into golf, you know, and I actually probably will".
"I actually think I will take more science classes".
"I actually think it will work," he says, picking up the phone.
"Ultimately, I actually think they will be happy with this book," he continued.
