Planning for 401k to Roth IRA conversion

Sure...if you use the Desktop software every year. After preparing the current year's data in the normal software, you can then use the What-If worksheet where you can transfer the current year's $$, into a second column for predicting the next year's situation...then change all the values for each of the next year's $$ categories to see what the tax hit ends up being for the additional amounts you want to convert, remove W-2 income, and can also check a box to use the next year's expected tax rates.

Issues?

1)  IF the 401k is a traditional pre-tax 401k, then most, or all of the $$ transferred to ROTH IRA will add to your other income (pension?) which bumps up your AGI and taxable income ....so it may not all be at the lowest tax rate...the actual % tax bracket will then depend total taxable income (after deductions)...and even that will vary too depending on what your filing status is (MFJ, or single?)

2)  You are not taking SS yet, but if you are also getting a pension to live on, and have started making Medicare payments too, if your income is too high for any one year (including those 401k-to-Roth conversions), then you could get hit with higher Medicare part B and D premiums the next year.  How much, again depends on whether you are single or married.....so pre-planning and dividing up the conversions over several years is usually preferable.

You can see the Medicare IRMAA tables here:

2023 Medicare Parts A & B Premiums and Deductibles 2023 Medicare Part D Income-Related Monthly Adjustment Amounts | CMS

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To get the What IF worksheet, after you fully fill in the current year's taxes in the desktop software, you need to switch to Forms Mode to be able to search for and open the What If worksheet.  Then work on that in Forms mode to plan and see the effect of varying the next year's 401k-to-Roth IRA conversion amounts.

There are so many moving parts here, you may want to see a financial planner.  Creating taxable income by doing Roth conversions will affect your medicare premiums and the taxability of social security (when you take it).  You are going to have some withdrawals already for living expenses, so you will have to plan carefully so that the extra you take out for conversion does not put you into too high a tax bracket.

Just as an example, if you are single and need $40,000 per year after tax to live, you will already be withdrawing $50,000 and pay 12% tax on everything over $15,000.  If you withdraw another $40K for conversion, that will be taxed at 22%.  However, if we suppose you receive $1000 per month in SS benefit, then at age 70 you would only need to withdraw $16,000 per year to make ends meet, which will almost be tax-free, or taxed at 10% or 15% instead of paying 22% now.

Also, I learned this when my mother developed dementia.  If you need to go into a nursing home, you must be "poor" for Medicaid to pick up the cost.  That means you get to keep $3000 and a car, and everything else goes to the government.  You turn over your assets, your pension and SS benefit, and only then, Medicaid will pick up the remainder.  But, as long as you turn over the RMD of your traditional IRA to the nursing home, you get to keep the principal of the IRA to use for whatever you want, or leave it to your kids.  But because Roth IRAs have no RMD, you have to turn over the entire amount before you get your nursing home covered.  It's years or decades away, but it's something to be aware of.  There's probably an argument that you need a well balanced portfolio of pre-tax assets, Roth assets, and non-protected investments.  good luck.