What is the difference between the billing date and the subscription date?

I'd like to know I'm I'm paying extra for only 4 days of service or 10ish days of service if I were to activate service options right now.

Look on that same page. Your estimated date of billing. If it's 4 days from now, then 4 days. If it's 10 days from now then 10 days.

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This is a general question, not an account specific question.

"estimated date of billing" is when your subscription renews.