{
  "generatedAt": "2026-09-08",
  "assumptions": {
    "iraLimit": 7500,
    "iraLimitSource": "https://www.irs.gov/newsroom/401k-limit-increases-to-24500-for-2026-ira-limit-increases-to-7500",
    "growthRate": 0.07,
    "capitalGainsRate": 0.15,
    "comparisonBasis": "Equal after-tax cost, with the nominal contribution limit binding on both"
  },
  "shelter": [
    {
      "rate": 12,
      "nominalLimit": 7500,
      "preTaxEquivalent": 8523,
      "extraShelterPct": 13.6
    },
    {
      "rate": 22,
      "nominalLimit": 7500,
      "preTaxEquivalent": 9615,
      "extraShelterPct": 28.2
    },
    {
      "rate": 24,
      "nominalLimit": 7500,
      "preTaxEquivalent": 9868,
      "extraShelterPct": 31.6
    },
    {
      "rate": 32,
      "nominalLimit": 7500,
      "preTaxEquivalent": 11029,
      "extraShelterPct": 47.1
    },
    {
      "rate": 35,
      "nominalLimit": 7500,
      "preTaxEquivalent": 11538,
      "extraShelterPct": 53.8
    },
    {
      "rate": 37,
      "nominalLimit": 7500,
      "preTaxEquivalent": 11905,
      "extraShelterPct": 58.7
    }
  ],
  "equalRates": [
    {
      "rateNow": 12,
      "rateLater": 12,
      "years": 10,
      "roth": 14754,
      "traditionalIra": 12983,
      "sideAccountNet": 1640,
      "traditional": 14623,
      "rothAdvantage": 131,
      "preTaxEquivalentOfRothLimit": 8523,
      "extraShelterPct": 13.6,
      "sideAccountTax": 131
    },
    {
      "rateNow": 12,
      "rateLater": 12,
      "years": 20,
      "roth": 29023,
      "traditionalIra": 25540,
      "sideAccountNet": 3095,
      "traditional": 28635,
      "rothAdvantage": 387,
      "preTaxEquivalentOfRothLimit": 8523,
      "extraShelterPct": 13.6,
      "sideAccountTax": 387
    },
    {
      "rateNow": 12,
      "rateLater": 12,
      "years": 30,
      "roth": 57092,
      "traditionalIra": 50241,
      "sideAccountNet": 5958,
      "traditional": 56199,
      "rothAdvantage": 893,
      "preTaxEquivalentOfRothLimit": 8523,
      "extraShelterPct": 13.6,
      "sideAccountTax": 893
    },
    {
      "rateNow": 12,
      "rateLater": 12,
      "years": 40,
      "roth": 112308,
      "traditionalIra": 98831,
      "sideAccountNet": 11590,
      "traditional": 110422,
      "rothAdvantage": 1887,
      "preTaxEquivalentOfRothLimit": 8523,
      "extraShelterPct": 13.6,
      "sideAccountTax": 1887
    },
    {
      "rateNow": 22,
      "rateLater": 22,
      "years": 10,
      "roth": 14754,
      "traditionalIra": 11508,
      "sideAccountNet": 3006,
      "traditional": 14514,
      "rothAdvantage": 239,
      "preTaxEquivalentOfRothLimit": 9615,
      "extraShelterPct": 28.2,
      "sideAccountTax": 239
    },
    {
      "rateNow": 22,
      "rateLater": 22,
      "years": 20,
      "roth": 29023,
      "traditionalIra": 22638,
      "sideAccountNet": 5675,
      "traditional": 28312,
      "rothAdvantage": 710,
      "preTaxEquivalentOfRothLimit": 9615,
      "extraShelterPct": 28.2,
      "sideAccountTax": 710
    },
    {
      "rateNow": 22,
      "rateLater": 22,
      "years": 30,
      "roth": 57092,
      "traditionalIra": 44532,
      "sideAccountNet": 10924,
      "traditional": 55455,
      "rothAdvantage": 1637,
      "preTaxEquivalentOfRothLimit": 9615,
      "extraShelterPct": 28.2,
      "sideAccountTax": 1637
    },
    {
      "rateNow": 22,
      "rateLater": 22,
      "years": 40,
      "roth": 112308,
      "traditionalIra": 87601,
      "sideAccountNet": 21249,
      "traditional": 108850,
      "rothAdvantage": 3459,
      "preTaxEquivalentOfRothLimit": 9615,
      "extraShelterPct": 28.2,
      "sideAccountTax": 3459
    },
    {
      "rateNow": 24,
      "rateLater": 24,
      "years": 10,
      "roth": 14754,
      "traditionalIra": 11213,
      "sideAccountNet": 3280,
      "traditional": 14493,
      "rothAdvantage": 261,
      "preTaxEquivalentOfRothLimit": 9868,
      "extraShelterPct": 31.6,
      "sideAccountTax": 261
    },
    {
      "rateNow": 24,
      "rateLater": 24,
      "years": 20,
      "roth": 29023,
      "traditionalIra": 22057,
      "sideAccountNet": 6191,
      "traditional": 28248,
      "rothAdvantage": 775,
      "preTaxEquivalentOfRothLimit": 9868,
      "extraShelterPct": 31.6,
      "sideAccountTax": 775
    },
    {
      "rateNow": 24,
      "rateLater": 24,
      "years": 30,
      "roth": 57092,
      "traditionalIra": 43390,
      "sideAccountNet": 11917,
      "traditional": 55307,
      "rothAdvantage": 1785,
      "preTaxEquivalentOfRothLimit": 9868,
      "extraShelterPct": 31.6,
      "sideAccountTax": 1785
    },
    {
      "rateNow": 24,
      "rateLater": 24,
      "years": 40,
      "roth": 112308,
      "traditionalIra": 85354,
      "sideAccountNet": 23181,
      "traditional": 108535,
      "rothAdvantage": 3773,
      "preTaxEquivalentOfRothLimit": 9868,
      "extraShelterPct": 31.6,
      "sideAccountTax": 3773
    },
    {
      "rateNow": 32,
      "rateLater": 32,
      "years": 10,
      "roth": 14754,
      "traditionalIra": 10032,
      "sideAccountNet": 4373,
      "traditional": 14405,
      "rothAdvantage": 348,
      "preTaxEquivalentOfRothLimit": 11029,
      "extraShelterPct": 47.1,
      "sideAccountTax": 348
    },
    {
      "rateNow": 32,
      "rateLater": 32,
      "years": 20,
      "roth": 29023,
      "traditionalIra": 19735,
      "sideAccountNet": 8254,
      "traditional": 27990,
      "rothAdvantage": 1033,
      "preTaxEquivalentOfRothLimit": 11029,
      "extraShelterPct": 47.1,
      "sideAccountTax": 1033
    },
    {
      "rateNow": 32,
      "rateLater": 32,
      "years": 30,
      "roth": 57092,
      "traditionalIra": 38823,
      "sideAccountNet": 15889,
      "traditional": 54712,
      "rothAdvantage": 2380,
      "preTaxEquivalentOfRothLimit": 11029,
      "extraShelterPct": 47.1,
      "sideAccountTax": 2380
    },
    {
      "rateNow": 32,
      "rateLater": 32,
      "years": 40,
      "roth": 112308,
      "traditionalIra": 76370,
      "sideAccountNet": 30908,
      "traditional": 107278,
      "rothAdvantage": 5031,
      "preTaxEquivalentOfRothLimit": 11029,
      "extraShelterPct": 47.1,
      "sideAccountTax": 5031
    },
    {
      "rateNow": 35,
      "rateLater": 35,
      "years": 10,
      "roth": 14754,
      "traditionalIra": 9590,
      "sideAccountNet": 4783,
      "traditional": 14373,
      "rothAdvantage": 381,
      "preTaxEquivalentOfRothLimit": 11538,
      "extraShelterPct": 53.8,
      "sideAccountTax": 381
    },
    {
      "rateNow": 35,
      "rateLater": 35,
      "years": 20,
      "roth": 29023,
      "traditionalIra": 18865,
      "sideAccountNet": 9028,
      "traditional": 27893,
      "rothAdvantage": 1130,
      "preTaxEquivalentOfRothLimit": 11538,
      "extraShelterPct": 53.8,
      "sideAccountTax": 1130
    },
    {
      "rateNow": 35,
      "rateLater": 35,
      "years": 30,
      "roth": 57092,
      "traditionalIra": 37110,
      "sideAccountNet": 17379,
      "traditional": 54488,
      "rothAdvantage": 2604,
      "preTaxEquivalentOfRothLimit": 11538,
      "extraShelterPct": 53.8,
      "sideAccountTax": 2604
    },
    {
      "rateNow": 35,
      "rateLater": 35,
      "years": 40,
      "roth": 112308,
      "traditionalIra": 73000,
      "sideAccountNet": 33806,
      "traditional": 106806,
      "rothAdvantage": 5502,
      "preTaxEquivalentOfRothLimit": 11538,
      "extraShelterPct": 53.8,
      "sideAccountTax": 5502
    },
    {
      "rateNow": 37,
      "rateLater": 37,
      "years": 10,
      "roth": 14754,
      "traditionalIra": 9295,
      "sideAccountNet": 5056,
      "traditional": 14351,
      "rothAdvantage": 403,
      "preTaxEquivalentOfRothLimit": 11905,
      "extraShelterPct": 58.7,
      "sideAccountTax": 403
    },
    {
      "rateNow": 37,
      "rateLater": 37,
      "years": 20,
      "roth": 29023,
      "traditionalIra": 18284,
      "sideAccountNet": 9544,
      "traditional": 27828,
      "rothAdvantage": 1195,
      "preTaxEquivalentOfRothLimit": 11905,
      "extraShelterPct": 58.7,
      "sideAccountTax": 1195
    },
    {
      "rateNow": 37,
      "rateLater": 37,
      "years": 30,
      "roth": 57092,
      "traditionalIra": 35968,
      "sideAccountNet": 18372,
      "traditional": 54340,
      "rothAdvantage": 2752,
      "preTaxEquivalentOfRothLimit": 11905,
      "extraShelterPct": 58.7,
      "sideAccountTax": 2752
    },
    {
      "rateNow": 37,
      "rateLater": 37,
      "years": 40,
      "roth": 112308,
      "traditionalIra": 70754,
      "sideAccountNet": 35737,
      "traditional": 106492,
      "rothAdvantage": 5817,
      "preTaxEquivalentOfRothLimit": 11905,
      "extraShelterPct": 58.7,
      "sideAccountTax": 5817
    }
  ],
  "crossover": [
    {
      "rateNow": 12,
      "rothWinsAtOrAboveRetirementRate": 11,
      "pointsOfDropThatRescueTraditional": 2
    },
    {
      "rateNow": 22,
      "rothWinsAtOrAboveRetirementRate": 20,
      "pointsOfDropThatRescueTraditional": 3
    },
    {
      "rateNow": 24,
      "rothWinsAtOrAboveRetirementRate": 21,
      "pointsOfDropThatRescueTraditional": 4
    },
    {
      "rateNow": 32,
      "rothWinsAtOrAboveRetirementRate": 28,
      "pointsOfDropThatRescueTraditional": 5
    },
    {
      "rateNow": 35,
      "rothWinsAtOrAboveRetirementRate": 31,
      "pointsOfDropThatRescueTraditional": 5
    },
    {
      "rateNow": 37,
      "rothWinsAtOrAboveRetirementRate": 33,
      "pointsOfDropThatRescueTraditional": 5
    }
  ],
  "caveats": [
    "A single contribution at a single growth rate to a single horizon.",
    "The taxable side account is buy-and-hold, taxed once at the end; annual dividend drag would widen the Roth's lead.",
    "Ignores RMDs, IRMAA, state tax and the Saver's Credit — all of which push toward Roth and none of which are modelled.",
    "Applies only to savers who actually max out. Below the limit the classic tie holds exactly, and that is the majority case."
  ]
}