Backdoor + Mega-Backdoor Roth Sequencer

Mega-Backdoor first — it's a much bigger number per year (typically $35,500 in 2026 vs $7,000 for the IRA Backdoor) and the §415(c) limit is calendar-year — unused room can't be carried forward. Do Mega-Backdoor by Dec 31 to capture the year, then do Backdoor IRA anytime (you have until April 15 of the following year for prior-year contributions).

IRC §408(d)(2) — when you do a Roth conversion of any Traditional IRA money, the IRS treats ALL your Traditional IRA balances as a single pool. Suppose you have $50,000 pre-tax in a SEP-IRA + $7,000 nondeductible from this year's Backdoor contribution. Pro-rata says 50/57 = 87.7% of any conversion is taxable. Doing a Backdoor here costs you ($7,000 × 87.7%) × your marginal rate ≈ $2,000 in conversion tax. That's the pro-rata 'break.'

Rolling your pre-tax Traditional IRA balance INTO your 401(k) before doing the Backdoor conversion. The §408(d) pro-rata pool is computed across IRAs only — 401(k) balances are NOT included. So once the pre-tax money is inside the 401(k), the Backdoor conversion pool is just your $7,000 of nondeductible basis, pro-rata is clean, and the conversion is $0 taxable. Requires that your 401(k) plan accepts rollovers IN — not all plans do.

You have three options: (1) skip the Backdoor IRA and rely on Mega-Backdoor only — most of the Roth capacity comes from Mega anyway; (2) ask your plan administrator to enable rollover-in (sometimes possible via plan amendment); (3) do a one-time Roth conversion on the entire pre-tax balance and pay the tax — clears the pool permanently. Option 3 is expensive but makes future Backdoor conversions clean forever.

You do not need the Backdoor at all — just contribute directly to your Roth IRA. The calculator detects this and shows the 'Direct Roth IRA' step instead. 2026 phaseouts: single $150k–$165k, MFJ $236k–$246k. Below the lower bound = full direct contribution; in the band = partial; above = backdoor required.

Both standalone calcs answer 'how much can I contribute via THIS path?' This sequencer answers the sequencing question — basis isolation order, which path to prioritise, and whether your plan setup blocks one of them. The total combined Roth-per-year figure is the headline you actually need for year-end planning.

For a $300k–$700k MFJ tech worker with: $23,500 elective deferral + $11,000 employer match + plan supports after-tax + plan supports in-service distribution: Mega-Backdoor ≈ $35,500 + Backdoor IRA ≈ $7,000 = $42,500/yr of new Roth space. Over a 30-year career at 7%: ~$4.3M of tax-free retirement savings on top of your regular 401(k).

No — they are separate buckets. The Roth IRA $7,000 limit (IRC §408A) and the §415(c) $70,000 cap (which controls Mega-Backdoor room) are distinct. You can fill both in the same year. The §402(g) $23,500 elective deferral limit is yet a third bucket, also separate.

Big match shrinks the Mega-Backdoor room dollar-for-dollar. Example: employer match $30,000 + elective deferral $23,500 = $53,500 used; §415(c) cap $70,000 leaves $16,500 of after-tax room. The math is fully mechanical — the calculator computes this for you.

In-plan Roth 401(k) conversion strategy (a different mechanic), governmental 457 plans, 403(b) considerations for non-profit employees, SEP-IRA / SIMPLE IRA contributions, conversions of OLD Traditional IRA balances (the one-time pre-Backdoor cleanup), and the conversion ladder strategy for early-retirement access (IRC §72(t)). For those, talk to a CPA who specialises in equity-comp + retirement planning — the Mathstub /about page links a CPA-matching affiliate.

No — it's a planning calculator. Real decisions depend on facts the calculator does not capture (state tax interactions, conversion-year vs. distribution-year planning, expected future marginal rate, plan-specific rules). For high-stakes decisions ($25k+ of Roth capacity at stake) engage a CPA or fiduciary planner.