Start with the next cap.
Our suggested workflow is to select one breakthrough before planning the entire build. You will get a short list that is easier to check against the game. This is a planning suggestion, not a claim about the most efficient upgrade for every character.
Add only the abilities you intend to upgrade.
Basic attack, battle skill, Ultimate and QTE each have their own current and target levels. Different targets can be calculated together in one plan; a skill with unchanged levels adds no upgrade cost. To check only a breakthrough, keep all four skill ranges unchanged. City-skill costs are excluded.
Take the list back to the game.
Copy or print the result. Your account stays in the game; the calculation stays in this browser. No login, bag upload or game connection is part of this flow.