Can I prepay my Turbotax fee now? or do I I have to wait until I file?

visit the Print Center and try to print your return.

TurboTax will ask you to pay.

Always print a copy of your completed tax return for your records, and review it carefully before e-Filing.
You will need it if you are audited by the IRS, or to amend if a TurboTax update changes your return or for any other reason,

AND, to find your AGI next year.