Can a request for an extension 2018 tax year to prepare?

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go to www.irs.gov/payments and "Make a payment"

select Reason: Extension

pay any amount ($5.00 will do}.   your request is automatically approved.

Make a note of your payment  amount so you can claim credit for that.

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the amount should be the balance of your tax liability to avoid penalties.
If you have to guess, overestimate. you'll get it back when you file.