For itemized deductions, do I need the exact amount? i.e. Medical bills

[MaryK4]

Yes, the IRS requires you to be able to substantiate (or prove) the amounts you are deducting so in general, estimates should not be used.  It might be okay if you have the records and receipts.  However, if you overestimate, you will pay less in taxes which is a form of tax evasion.

[CSKcpa56]

taxpayers are always required to keep records supporting their deductions. I'm not sure why you wouldn't have the exact amount. individuals can (normally) only take deductions for what they paid for. Course "paid for" can include medical expenses you put on a credit card - it doesn't matter if the credit card was paid. For example if you were in the hospital and they charged you $10K and your insurance company paid $9K you would owe $1K. Can't take a deduction for the $1K until you pay for it or put it on a credit card.