(i) The actual truth of Q.
This is just to say that I will happen to φ.
(ii) Determinism about Q
This adds the claim that the conjunction of some past state P0 and the laws of nature L together entail that I will φ. Not only is Q actually true, but its negation is inconsistent with P0 & L. So in this sense I must φ. But I may retain some causal responsibility, in the sense that if I had been different, so would have been the outcome. It's merely the case that (given P0 and L) I could not have been different in the first place.
(iii) Fatalism about Q
This adds the yet further claim that Q is robustly overdetermined, such that I still would have ended up φ-ing even if my thoughts, desires, and intentions had somehow been different. So even various alternative past states P1, or P2, etc., when conjoined with L, entail Q. If it hadn't happened the one way, it would have happened some other way. This yields a much stronger sense in which I 'must' φ: even had things been different, my φ-ing could not have been avoided.
These various modalities are often confused. So it is important to be clear that just because something will occur, does not mean that there is any stronger sense in which it 'must' or is 'guaranteed' to occur. If you know beforehand, it may be 'certain' in an epistemic sense. But that is of no interest here; what matters is the metaphysical question of how things are in themselves. Compare the past: we may have certain knowledge that some past event E occurred, but that alone does not mean that E itself was in any way guaranteed or 'fated' to occur. As things turned out, E did occur, but that fact is obviously compatible with the claim that things could have turned out differently. And exactly the same is true of future events, such as my φ-ing. Actuality does not imply necessity; 'is' (or 'will') does not imply 'must'.
(In practice, others will rarely be in a position to safely assert 'Richard will φ' in advance unless I am unable to do otherwise. After all, how else can they be so sure? I might change my mind -- especially if I overhear them, I might change my mind simply to prove them wrong! So, in practice we are used to 'will' assertions being correlated with 'must' facts. This practical correlation might help explain why we are so easily tempted to conflate the two ideas, but clear thinking requires us to disentangle such associations.)
One may object (as did my confused past self, circa 2004): "If Q is true, then I cannot actually fail to φ, for that would render Q false, contrary to the assumption." But this is deceptive rhetoric. It is true, but utterly trivial, that one cannot hold the truth of Q fixed and at the same time make it false. But there is no substantive necessity here. For all that's been said, it might be entirely within my power whether I φ, and hence whether Q is actually true or false. If Q is actually true, then that's just to say that I won't actually fail to φ, but it says nothing about what I could have done. Don't let the order of words on the screen fool you: the direction of explanation flows from my contingent action to the truth of the proposition. (Q is true because I φ. It would get things backwards to think that I φ because Q is somehow antecedently true.)
A related caution: it may be true (now) that tomorrow I φ. But that makes it sound like the truth exists prior to the event. This is, again, a mere quirk of language. To say it's true that tomorrow I φ is simply to say that tomorrow I φ. It's a claim about tomorrow's events, and whether it's true or not depends entirely on those events. If it turns out that I φ, then we can say it was "true" all along. But you shouldn't be tempted to read anything deeper into such claims. (In particular, it's not to say the future truth is somehow 'contained within' or derivable from the present state of affairs -- determinism is a further claim!)
A final source of confusion stems from conflating descriptive and rigidly designating interpretations of 'the actual world'. Let '@' rigidly designate what philosophers call "the actual world" (and what really means the actual world-description, or a complete list of all the propositions that happen to be actually true). Now one might worry that it's a necessary truth that Q is true in @ -- or that 'actually Q' expresses a necessary truth. So we lack the power to change what's true in the actual world (@); but the actual world is the world we care about, so (the argument goes) we lack the only power we ever cared to have.
Can you spot the fallacy? We are not essentially concerned with @ -- in itself, @ is a mere world-description, a way the concrete universe could be. What we care about is the concrete universe, and how it turns out. In particular, if the universe turns out as @ describes (so that @ is the "actual world[-description]") then we care about that, for the universe's sake. Note that the power we're really concerned with is the power to change the universe, not some particular description thereof. In short: we can't change the description (de re) of the universe, but we can change the universe itself so that it meets a different description. And of course it's the latter power that we really cared about all along.