～るまでだJust, Merely, Simply, Only

These are essentially the same grammar pattern, with the difference in nuance coming from the verb tense. ～たまでだ is typically used to downplay a completed action, e.g. 自分の意見を述べたまでだ ('All I did was express my opinion.), while ～るまでだ generally implies the speaker will 'just do (something)' in the face of a bad situation, e.g. 誰も教えてくれないなら、自分で調べるまでだ ('If no one will teach me, I'll just look it up myself'). Both are typically used to refer to one's own actions or those of someone in one's in-group.

Both involve a limit, but the type of limit is different. それまでだ is an evaluative expression meaning “that’s the end,” used to judge that nothing more can be done if a crucial condition is lost, as in 信頼を失ったらそれまでだ (‘If you lose trust, that’s the end.’). By contrast, Vるまでだ (and までのことだ) expresses resignation, meaning “one can only but (B),” often used with なら to show that (B) is the only remaining option in a negative situation, as in 誰にも教えてもらえないなら、ネットで調べてみるまでだ (‘If no one will teach me, I’ll just have to look it up online.’).