A while back I wrote here that I was turning my Excel model into free Roth conversion software — and that post promised “coming soon.” It’s no longer coming; it’s live and free to use. No signup, no download, no spreadsheet skills required: enter your numbers in the browser, click optimize, and a real solver plans your conversion schedule year by year.
From a personal Excel model to software anyone can run
This started as the workbook I built for my own retirement planning — a linear program wired into Excel that decided how much to convert each year. It worked, but it had the classic Excel problem: I couldn’t hand it to anyone without a lecture about solvers and plugins. So I rebuilt it as a web app, the same way I’ve been converting my other optimization models. The porting had its own lessons (I wrote up what I learned building the Roth conversion optimizer if you enjoy the behind-the-scenes), but the short version: the mathematics moved intact, and the spreadsheet stopped being a prerequisite.
What the software actually does
Most free Roth calculators answer one narrow question — “if I convert X this year, what’s the tax?” This one treats retirement cash flow as a single optimization problem, because that’s what it is. Every year of your plan, money has to come from somewhere: living expenses get funded, taxes get paid from some account, required minimum distributions happen whether you like them or not, and conversions compete with all of it for space in your tax brackets. The optimizer decides the conversion schedule, the withdrawal order, and which account pays each bill — simultaneously — to maximize what you actually keep: after-tax wealth at the end of your horizon.
It also handles the pieces that usually get ignored: your taxable brokerage account with its cost basis, long-term and short-term gains taxed at their own rates; Social Security timing; and a “spend it down” mode that flips the question around — instead of maximizing what’s left, it finds the highest constant annual spending that drains every account to roughly zero by your end age, die-with-zero style. If you want the math itself, I laid out the linear program behind the calculator in a separate post.
What it doesn’t do — read this part
Honesty section. State tax is one flat rate you enter, not your state’s actual brackets. IRMAA Medicare surcharges, the Net Investment Income Tax, and ACA subsidy cliffs aren’t modeled — and for some households those change the answer. It uses one real rate of return across accounts. And it is not financial or tax advice: it’s a well-built starting point that shows you the shape of a good plan, which you should stress-test with a CPA or planner before moving real money. The IRS’s own Roth IRA rules are the canonical reference for what conversions actually require.
What a typical result looks like
The pattern the optimizer finds for many early retirees is the one the theory predicts, but with the amounts made concrete: in the gap years — after the paycheck stops, before Social Security and required minimum distributions arrive — taxable income is unusually low, and the plan concentrates conversions there, sized to fill the brackets you choose to tolerate and not a dollar more. Then Social Security starts, the low-bracket window narrows, and conversions taper. What surprises people is the second-order stuff: which account pays the conversion tax changes the optimal amounts, and a modest change in living expenses can move thousands of dollars of conversions between years. You don’t see those interactions in a rule of thumb; you see them in a solved plan.
Common questions
Is it really free, and what happens to my numbers? Free, no account, no trial clock. The numbers you type are used to run your solve and aren’t tied to any identity — there’s no login to tie them to.
Why should I trust a free tool from a stranger on the internet? Fair question, and my honest answer: don’t trust it — check it. The full mathematical formulation is published in the model write-up, so the logic is auditable rather than a black box, and the output is a plan you can hand to a professional to verify. A tool that shows its math is asking for scrutiny, not faith.
I write about FIRE — can I put this on my site? Yes. The calculator has an embed version built for exactly that; the embed snippet is on the tool page itself. It stays free for your readers too.
How to use it in ten minutes
You enter your situation once: ages and horizon, balances in traditional, Roth, and taxable accounts (with basis), expected income and Social Security, living expenses, and the rates you want assumed. Click optimize and read the year-by-year table: conversion amount, withdrawals by account, taxes, and ending balances per year. The interesting part is rarely the first run — it’s changing one assumption and watching the plan reshape. Delay Social Security two years, or add a what-if future tax increase, and you’ll see the conversion window move in a way no rule of thumb would have told you. Run it three or four times with different assumptions before you conclude anything — the comparison between runs teaches more than any single answer, and it costs you nothing but minutes. That interplay is the whole reason this needed to be an optimizer and not another when-does-a-conversion-make-sense article — though I wrote that one too, and the two work well together.
The software is free because these tools are working demonstrations of what I’ve built over an optimization career, and because the FIRE community — where I picked up half my ideas — runs on people sharing their homework. If it helps you, the best repayment is telling the next person who’s hand-rolling this in a spreadsheet: roth-conversion-calculator.kindoflost.com.
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