Attached is an excel sheet you can use to discover the percent of new automatic transmission fluid after each drain and fill. You will need to plug in the drain volume and overhaul volume for your specific car in the file (click the Enable Editing at the top of this file page first). The example numbers are for my 2013 CRV (81K miles). I stopped at 7 drain and fills (96.15% new ATF). Keep in mind that you must let the newly added ATF mix after each drain and fill. You can search the forum on how to do this. I did mine after a highway drive to my closest city (60 miles) and back because this was convenient for me.
The cost for me for 7 drain and fills was ~$108 and the quote for one drain and fill from the dealer was $150. I bought Honda DW-1 ATF from the dealer. A case plus 4 quarts (16 quarts total). When you buy from the dealer ask for a discount. They always give me a discount. The regular price at the dealer was $8.25/quart but the discounted price is $6.75/quart.

 

Generally speaking, draining the ATF 3 times and refilling with about 3-quarts each time is considered to be about a 90% replacement of your ATF; this type of a service is often referred to as a 3x3 ATF replacement and is very common in the Honda world.

 

This is very dependent on the drain and overhaul volume ratios. This spreadsheet will clear that up for everyone.

 

No need to overthink it, the 3x3 has been in play with Honda transmissions for decades and is tried and true.