@KU-Jayhawk if you are using the downloaded/CD version of 2019 TurboTax, the facility already exists ( has existed for many years ) ---- after entering the data , right click while still in the entry box, from the drop- down list select "mark entry as estimate " --- the data on the form would have different color font and when doing final checks, it will not allow you to file till you clear the "estimated" flag. This works in the current version and I have used it for years to estimate.
God Luck
