After looking at NewRetirement's 2023 Roth Conversion Calculator, I cover some "runners-up," including one from Fidelity and another from Schwab. You can try them out for yourself:

https://www.fidelity.com/calculators-...
https://www.schwab.com/ira/ira-calcul...

https://www.calcxml.com/calculators/r...

https://www.newretirement.com/retirem...

Note, I'm not a professional. I have no initials after my name. So take these as entertaining ideas from one educated consumer to another. Always do your own due diligence and seek out a professional if you need one.