I actually just went through this last night with turbo tax. They need the full amount of what you are writing off and then they will break it down to the 80% maximum, and take out the 2% “upper limit” also. The only thing you need to do is to either take the standard $51 per day or find the daily rates for each city you overnighted in. I made a spreadsheet to keep track of all of this.

Only other thing is the first and last days of your trip aren’t considered full days so you need to reduce your rates to 75% for them. Once you put in the total claiming and the total you were paid, the system subtracts the 2 and gives your final write off total.

Like most said now, unless you have a bunch of other write offs, next year when the standard deductions double this is probably going to not be worth the hassle. And honestly don’t even know if it’s allowed in the new tax code.

Feel bad for the perdiem tax calc site, as they are going to lose a lot of business starting next year.