Free Roth conversion calculator
A Roth conversion calculator helps you decide how much of your traditional 401(k) or IRA to move into a Roth — and when. Done in the right years, conversions fill up low tax brackets on purpose, shrink the required minimum distributions (RMDs) that can spike your taxes later, and leave tax-free money to your heirs. Coastline models conversions inside a full multi-decade tax projection, so you can see the lifetime effect rather than just this year's bill.
The conversion window, stage by stage
A Roth conversion is only worthwhile if you convert at a lower rate than you'd otherwise pay later. That makes timing everything, and it tracks your income across retirement:
| Stage | Taxable income | Conversion room |
|---|---|---|
| Early retirement (before SS & RMDs) | Low | Large |
| After claiming Social Security | Higher | Smaller |
| After RMDs begin (73/75) | Highest | Little |
The takeaway: the quiet, low-income years right after you retire are the cheapest time to convert. Wait until Social Security and RMDs stack up and the same conversion costs far more.
Why conversions pay off
- Defusing the RMD "tax torpedo." A large traditional balance keeps compounding until age 73 (75 for those born in 1960+), when RMDs force taxable withdrawals — often larger than you need, landing on top of Social Security. Converting earlier shrinks that future forced income.
- Bracket filling. If a low-income year leaves room in the 10%, 12%, or 22% bracket, converting just enough to "fill" it moves money to tax-free growth at a rate you may never see again.
- Tax-free to heirs. Under the 10-year rule, most non-spouse heirs must empty an inherited traditional IRA within a decade — often in their peak earning years. A Roth passes the same wealth tax-free.
- A conversion ladder for early retirees. Converted amounts can be withdrawn penalty-free five years later, which is a common way to bridge income before age 59½.
The costs to weigh
Conversions aren't free money. The converted amount is taxable income in the year you convert, so a good calculator has to weigh it against real second-order effects: a bigger conversion can raise your ACA health-insurance cost (marketplace subsidies shrink as income rises), push part of a Social Security benefit into taxation, or lift Medicare premiums (IRMAA) two years later. The art is converting enough to lower lifetime tax without tripping those thresholds — which is exactly the kind of multi-year trade-off Coastline is built to show.
Why Coastline's version is different
Most free calculators hand you a single headline number with the assumptions hidden. Coastline is built the opposite way:
- Real tax math, not a flat rate. It applies federal and state income tax, long-term capital-gains rules, and account-by-account treatment (taxable, traditional, Roth) — in both your working years and retirement.
- The whole journey. It models accumulation (saving and investing) and drawdown (spending it down), so you see how the plan connects end to end, not just one half.
- The math is shown. Every figure has a click-through breakdown of how it was computed — a level of transparency even paid tools rarely expose.
- US and Canada. It natively handles Canadian plans (RRSP, TFSA, CPP, OAS) alongside US accounts, which most calculators ignore.
- Free, no signup. No account, no email, no account-linking. Your inputs run the projection and are then discarded.
This is educational, not tax advice — conversion math is personal and the rules change. Model your own brackets, ACA and IRMAA thresholds, and RMD horizon in the calculator, and confirm current rules with a professional before converting.
Common questions
What is a Roth conversion calculator?
A tool that estimates the tax cost and long-term benefit of moving money from a traditional 401(k) or IRA into a Roth. Coastline models conversions inside a full multi-decade projection, so you see the lifetime effect on taxes, RMDs, and heirs — not just this year’s bill.
When is the best time to do a Roth conversion?
Usually in the low-income years after you stop working but before Social Security and required minimum distributions begin, when converting fills up low tax brackets at bargain rates.
What is the RMD tax torpedo?
A large traditional balance keeps growing until RMDs begin at 73 (75 for those born in 1960 or later), then forces taxable withdrawals that can stack on top of Social Security and push you into higher brackets. Converting earlier shrinks that future forced income.
Do conversions affect my health insurance or Medicare?
They can. A conversion raises taxable income, which can reduce ACA marketplace subsidies now or raise Medicare premiums (IRMAA) two years later. A good plan converts enough to lower lifetime tax without tripping those thresholds — which Coastline helps you see, for free and with no signup.