{
  "slug": "backdoor-roth-pro-rata",
  "title": "Backdoor Roth Pro-Rata Tax Calculator",
  "heading": "Backdoor Roth Pro-Rata Rule Calculator",
  "category": "financial",
  "url": "https://www.revenuelab.fyi/toolbox/backdoor-roth-pro-rata",
  "summary": "Find the taxable share of a backdoor Roth conversion when you hold pretax IRA money.",
  "description": "The backdoor Roth strategy — contribute nondeductible dollars to a traditional IRA, then convert to Roth — only works cleanly if you have zero other pretax IRA balances. If you hold any pretax traditional, SEP, or SIMPLE IRA money, the IRS pro-rata rule forces you to treat every conversion as a proportional mix of pretax and after-tax dollars across all your IRAs, not just the account you just funded. This calculator applies IRS Form 8606 logic: it totals all your traditional-type IRA balances (aggregated), figures out what fraction is your basis (nondeductible contributions), and shows exactly how much of your intended conversion is taxable income this year versus tax-free return of basis. Getting this wrong is one of the most common backdoor Roth mistakes, and it usually surprises people who forgot about an old rollover IRA sitting from a prior employer's 401(k).",
  "formula": "Nontaxable ratio = total basis ÷ total year-end IRA balance (across all traditional/SEP/SIMPLE IRAs). Taxable amount converted = conversion × (1 − nontaxable ratio).",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=backdoor-roth-pro-rata",
  "inputs": [
    {
      "id": "basis",
      "label": "Total nondeductible basis (all IRAs)",
      "kind": "number",
      "hint": null,
      "default": 7000,
      "unit": "$",
      "min": 0,
      "max": null
    },
    {
      "id": "totalBalance",
      "label": "Total traditional/SEP/SIMPLE IRA balance (year-end, incl. this contribution)",
      "kind": "number",
      "hint": null,
      "default": 57000,
      "unit": "$",
      "min": 1,
      "max": null
    },
    {
      "id": "conversionAmount",
      "label": "Amount you plan to convert",
      "kind": "number",
      "hint": null,
      "default": 7000,
      "unit": "$",
      "min": 0,
      "max": null
    }
  ],
  "outputs": [
    {
      "id": "taxablePortion",
      "label": "Taxable amount of conversion",
      "format": "currency",
      "hint": null,
      "primary": true
    },
    {
      "id": "nontaxablePortion",
      "label": "Tax-free amount of conversion",
      "format": "currency",
      "hint": null,
      "primary": false
    },
    {
      "id": "nontaxableRatioPct",
      "label": "Nontaxable ratio (Form 8606)",
      "format": "percent",
      "hint": null,
      "primary": false
    },
    {
      "id": "remainingBasis",
      "label": "Basis remaining after conversion",
      "format": "currency",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Total nondeductible basis (all IRAs): 7000 $",
      "Total traditional/SEP/SIMPLE IRA balance (year-end, incl. this contribution): 57000 $",
      "Amount you plan to convert: 7000 $"
    ],
    "outputs": [
      "Taxable amount of conversion: $6,140",
      "Tax-free amount of conversion: $860",
      "Nontaxable ratio (Form 8606): 12.3%",
      "Basis remaining after conversion: $6,140"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter total nondeductible basis (all iras) ($).",
      "Enter total traditional/sep/simple ira balance (year-end, incl. this contribution) ($).",
      "Enter amount you plan to convert ($).",
      "Read your taxable amount of conversion on the right — it updates as you type.",
      "Hit Share to keep the scenario or send it to someone."
    ]
  },
  "scenarios": [
    {
      "name": "Conservative",
      "description": "Lower-end numbers — what if things land soft?",
      "values": {
        "basis": 4200,
        "totalBalance": 34000,
        "conversionAmount": 4200
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "basis": 7000,
        "totalBalance": 57000,
        "conversionAmount": 7000
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "basis": 11200,
        "totalBalance": 91000,
        "conversionAmount": 11200
      }
    }
  ],
  "limitations": [
    "Results are estimates before tax, fees, and inflation unless an input explicitly covers them.",
    "Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.",
    "This is educational maths, not financial advice. Check anything contractual with the lender or your accountant."
  ],
  "faq": [
    {
      "q": "Does the pro-rata rule count my Roth IRA balance?",
      "a": "No. Only traditional, SEP, and SIMPLE IRAs are aggregated for pro-rata purposes. Roth IRA balances and 401(k)/403(b) balances at an employer plan are excluded from this calculation entirely."
    },
    {
      "q": "How do people avoid the pro-rata problem?",
      "a": "The common fix is a 'reverse rollover': move existing pretax traditional IRA money into your current employer's 401(k) if the plan accepts incoming rollovers, leaving your traditional IRA balance at zero before you do the backdoor Roth. Once no pretax IRA balance exists, conversions are basis-only and fully tax-free."
    },
    {
      "q": "What if I forget an old IRA and get this wrong?",
      "a": "The IRS will tax the pro-rata share as income regardless of which account you think you converted, and you'll likely need to amend Form 8606. Check every 5498 and old employer rollover before doing a backdoor Roth."
    },
    {
      "q": "Does the pro-rata calculation use my balance before or after the conversion?",
      "a": "It uses the year-end balance across all traditional IRAs, which by IRS convention includes any amount converted during the year added back in for the ratio, per the Form 8606 worksheet. This calculator's 'total balance' input should be your year-end balance before subtracting the conversion."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/mega-backdoor-401k-capacity",
    "https://www.revenuelab.fyi/toolbox/hsa-triple-tax-advantage",
    "https://www.revenuelab.fyi/toolbox/inherited-ira-10-year-rmd"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Backdoor Roth Pro-Rata Tax Calculator (https://www.revenuelab.fyi/toolbox/backdoor-roth-pro-rata)"
}