To have a rough idea or estimation (about a situation, cause, price, etc.).
故障の原因はだいたい見当がついたので、部品を注文します。
I have a rough idea of the cause of the failure, so I'll order the parts.
この問題の解決方法が見当がつかない。
I have no idea how to solve this problem.
彼の年収は見当がつくが、正確な額は分からない。
I can guess his annual income roughly, but I don't know the exact amount.
見当がつくなら早めに教えてください。
If you have a rough idea, please tell me as soon as possible.