Does anyone replicate their IRS tax return?

I have a US/UK tax expert prepare my tax returns for me.  He’s not cheap and my taxes are reasonably simple, but having returned to the UK from the States only two years ago I wanted to ensure my taxes were being done correctly.  However I think next year I might consider doing the filing myself.  Income would be UK state pension and US Social Security for my wife and I, as well as a small company pension and perhaps an IRS distribution and some Roth conversions.

I have thought of trying Turbotax in parallel with my guy - and just not filing myself - just so I can replicate my guy’s numbers.  But I’ve also come across the tax spreadsheets of Glenn Reeves (https://sites.google.com/view/incometaxspreadsheet/home/download) which look pretty useful.

What software/websites have others used to replicate the IRS filing of their tax preparers?

I use TurboTax, download version which I also use to file taxes for my son.  His taxes are simple, no need for a tax preparer but my wife and I have much more complicated taxes so use a dual qualified tax preparer.  The download version of TT costs me about $55 but that includes State and I do file our State return directly as that is simple.

I use my downloaded version myself, replicating what my preparer does and can do some tax planning ahead of time.  Also, the London based tax preparer cannot file electronically so I use TT to e-file  and save the aggravation and cost of sending in a paper copy.

I use Free Fillable Forms from

https://www.irs.gov/e-file-providers/free-file-fillable-forms


You enter your info into the standard IRS forms. If you know what forms you need and you have a template for what goes where, it's straightforward. I had trouble with TurboTax and the like in paying for it, entering my foreign address and it not producing the right forms among other troubles. With the fillable forms, you are in command. They do check your arithmetic and complain if you miss an expected field, but they don't give you advice. You can then e-file for free.