How to ask a date why they're being vague about weekend plans

Look at how they've been texting for the last few days, not just this one message. If they've been quick and warm and the vague answer is an outlier, they probably just don't know their weekend yet, and a plain question will settle it. If replies have been getting shorter, slower or more flat over the past week, the vagueness is part of a pattern and you should weigh it that way. Also notice whether they've offered anything at all, even a maybe. Someone who says "I'd like to see you, I just don't know my Saturday yet" is in a very different place from someone who answers every suggestion with "we'll see" and never picks a day.

Don't try to decode the exact reason. You will get it wrong. Your job is to find out whether they want to make a plan, and the only reliable way to find that out is to ask about the plan itself.

A good question names a specific thing you'd like to do and asks whether it fits. Something like asking if Saturday evening works for a drink, or whether Sunday lunch is more their speed. Keep it to one question, so they only have to answer one thing. Once you add a second question, like "and what's going on with you?", the message turns into an interview and they'll answer the easier half.

Give them a clear easy out in the same message. You can say "no worries if the weekend's packed" or "happy to do a weeknight instead." That lets them say no without it feeling awkward, which makes a real yes more likely. People who feel cornered by a question give vague answers. People who feel free to decline are more likely to give you an actual answer.

Send the question in the late morning or early afternoon on a weekday, when people are more likely to pick up their phone and answer. Sending it at 11pm on Thursday puts it in front of them while they're half asleep and the answer will be lazy. Sending it on Friday afternoon leaves almost no time to plan, so they'll either ignore it or say "probably not."

If there's no reply within about a day, send one short follow-up that's easy to answer, such as a yes/no about one specific slot. If that also goes unanswered, stop chasing. Let the thread sit. If they come back later with a plan, you can answer warmly. If they don't, you've learned what you needed to know and you can move on without sending a third message.