what is difference between I have to go and I will have to go

"I have to go" this sentence is use in present perfect tense. That means you wanna go right now. "I will have to" this sentence is use in future perfect tense. That means you wanna go a few times later or in future.

first sentence shows present perfect tense and second shows future perfect tense.

I have to go. - simple present tense I will have to go. - simple future tense