Charge Magic

I think this spell would be more balanced if it was a d4 and required concentration, like guidance.

Firstly, let me say I appreciate your constructive criticism! I do disagree about a few points thought. I might be willing to change it to a d4, but in my own opinion, making it require concentration is pointless since it takes your entire action to cast this spell. At that point you might as well just cast whatever spell you wanted twice and hope the enemy fails the save, or you roll good enough to hit them.

Guidance is fine because it only works for ability checks, which are quite limited in what they can achieve. Having that cantrip last a minute with concentration makes sense, in the event the target is trying to make an extended check. Bless works for attack rolls and saving throws for the same duration and for three targets, but its a 1st level spell.

Those are also both spells that wizards, sorcerers, and warlocks can't cast. I imagine these three caster classes as being a bit more self-centered than clerics. As a general rule, they are interested in their studies, their inborn powers, or gaining power for themselves by effectively buying in exchange for tribute. Warlocks would especially benefit from this, since they have very few spell slots. Making that witchbolt connect means a lot more when you have two spell slots and that's it.

I also don't want to make the spell a bonus action to cast, because that would be incredibly overpowered. I don't want to extend the duration, because this cantrip affects any spell that the wizard, sorcerer, or warlock can cast. That is a massive amount of versatility. Any spell, +1d4 to hit, damage, or save DC. I wanted to give those caster classes a way to give their magic a little more oomf-- if they can plan properly. Because it takes an action to cast, a squishy wizard might not feel safe enough to cast charge magic  while Strahd von Zarovich is only 25 feet away. I have personally found it to be quite balanced in my playtests. I always encourage my players to try out my homebrew and critique me.

I do want to hear more of your thoughts though. Is there a recurring problem you've been experiencing with the spell?

Hearing you explanation has convinced me that this spell is pretty balanced. Usually I think things through better, so I apologize for misjudging this spell. 

I don't have any problems with this spell, I think I was just sleep deprived at the time and overlooked the casting time.

Oh, okay. Well, neat! I appreciate your input. If you ever have comments, criticisms, or questions, please don't hesitate to voice them! As long as discourse stays civil, I'm happy to talk whenever I'm available.

Be sure to get some good sleep, too. You die if you hit 6 levels of fatigue!