It would have to be some formula allowing input for tax rates at conversion and at an alternative future withdrawal year. I’ve given up on convincing math-challenged people that any amount taxed at a given rate today and then compounded any given number of years, is equal to the same amount compounded and then taxed at the same  rate in the same number of years.

High school kids in coding class could probably write the program if you gave them some word problems. “If John lives in California or New York and does a Roth conversion while paying 9% state tax, how much does he lose by not waiting until he moves to Nevada or Florida?” “If Mary is in a 24% tax bracket now and does a Roth conversion, how much does it cost her by not waiting until she moves into a nursing home and medical expenses leave her in a zero bracket?”

Since future tax rates are unpredictable, it’s mostly guess not science. There are some people who know their tax rate will increase at retirement, or know that a few thousand less in IRA distributions will save them from a 50% surcharge in Medicare premiums. But those are still questions best solved by human brains.