---
title: "Federal tax cost of a Roth conversion in one year: the extra income tax from stacking the converted amount on top of your other taxable income, with the marginal rate before and after."
method: POST
path: "/v1/retirement/roth-conversion"
tags: ["Retirement"]
---

# Federal tax cost of a Roth conversion in one year: the extra income tax from stacking the converted amount on top of your other taxable income, with the marginal rate before and after.

`POST /v1/retirement/roth-conversion`

## Request

- Base URL: `` (relative, and it does not resolve against the document’s source URL)
- URL: `/v1/retirement/roth-conversion`
- Auth: none declared

Federal tax cost of a Roth conversion in one year: the extra income tax from stacking the converted amount on top of your other taxable income, with the marginal rate before and after.

Payment: x402 ($0.10 USDC on eip155:8453). Call unpaid to receive an HTTP 402 with requirements, then retry with the PAYMENT-SIGNATURE header. Method: tax = federalTax(otherTaxable + conversion) - federalTax(otherTaxable); effective conversion rate = tax / conversion

## Request body

- object
  - `conversionAmount` number, required
  - `filingStatus` 'single' | 'mfj'
  - `otherTaxableIncome` number

## Response `200`

Verified result + provenance (formula, sources, reproducible SHA-256 hash).

## Other responses

- `400`: Invalid input (no charge) — body echoes the JSON Schema.
- `402`: Payment required — PAYMENT-REQUIRED header carries the x402 accepts[] quote.

---

[API](https://skmtc.dev/x402toll/apis/tollbooth-verified-calculators-for-ai-agents.md) · [All operations](https://skmtc.dev/x402toll/apis/tollbooth-verified-calculators-for-ai-agents/llms.txt) · [OpenAPI document](https://skmtc.dev/x402toll/apis/tollbooth-verified-calculators-for-ai-agents/revisions/60cb70a3e1a5?raw)