You will have to Vs Have to
Solution 1:
Will generally speaks to the future, so:
- "You will have to do that" implies that at some point in the future, it will be required, and that it isn't required now.
- "You have to do that" implies current, and is a requirement now, whether that requirement continues to be present in the future is unspoken.
Solution 2:
You will have to do that
This is the future tense. You will need to.
If you want to lose weight, you will have to eat less or exercise more.
You have to do that
This is the present tense. You need to/ you must.
To lose weight, you have to eat less or exercise more.
Solution 3:
The expression for obligation and necessity for both PRESENT and FUTURE is "Have to".
The difference between them, for clarification purpose or for avoiding confusion, is the time expression.
- I have to finish this job now. -- Present
- I have to finish this job by next Saturday. -- Future
However, the obligation in both cases exists at the speaking moment, even if one of them will be accomplished in the future time.
On the other hand, "Will have to" is the expression for obligation and necessity used with a conditional structure "Future Possible".
If my boss calls me tonight, I will have to work (tomorrow).
In the sentence above, the obligation for working tomorrow DOES NOT exist at the speaking moment; the obligation will be in force only if the condition if my boss calls me... becomes true. This means that there is no present obligation.