Why the site exists
A backdoor Roth question often sounds simple: if a contribution was already taxed, why does a conversion appear taxable? The answer can depend on other IRAs, contribution dates, prior basis, year-end values and the difference between contribution and conversion reporting. Generic instructions and brokerage screens do not always make those relationships visible. RothProRata.com was built to put the assumptions beside the result so a reader can understand the calculation instead of copying an unexplained number.
The site combines an ordinary IRA allocation calculator, Form 8606 planning preview, strategy comparison, basis records, document checklist and educational articles. These resources are intended to support a better-informed conversation with a qualified tax preparer or plan administrator. They are not a substitute for that person's review of actual records. A browser cannot verify an account's history, decide whether a receiving plan accepts a rollover, or determine every consequence on a complete federal and state return.
Who owns the publication
Moss Ladder owns and maintains the website and its public explanations. Editorial questions, correction requests and technical feedback can be sent to contact@mossladder.com. The contact page can prepare an email draft without submitting its contents to the website. Please use fabricated examples rather than tax returns, account numbers or Social Security numbers when describing a problem. A public operator name identifies responsibility for the publication; it does not imply an IRS relationship or a professional tax credential.
The editorial process uses AI-assisted drafting and engineering tools, with source links and reproducible examples supplied for readers to inspect. The editorial policy explains that process and the correction page records material changes. No custodian, plan provider or government agency has endorsed the publication. Source citations identify the authority being discussed, while the site's interpretation and examples remain the responsibility of the maintainer. Readers should follow the linked official documents when preparing an actual return.
How calculations are grounded in sources
The ordinary pro-rata model is cross-checked against the aggregation framework in Internal Revenue Code § 408(d)(2), the published 2025 Form 8606 and its instructions. Publications 590-A and 590-B provide context for contributions, rollover eligibility, distributions and Roth rules. The annual contribution limits are tied to IRS Notices 2024-80 and 2025-67, while federal ordinary-income bracket data is tracked separately by tax year. A reference to the 2026 limits is not presented as proof that final 2026 form instructions are available.
Worked examples identify one owner, the contribution year, prior basis, net conversion, applicable year-end value and any relevant other distributions. Where a table is generated by the existing engine, the prose explains the same arithmetic independently. A $7,000 basis and $28,000 pool produce a 25% ratio, for example. The purpose is to make an inconsistency visible rather than ask readers to trust a calculator label. Specialist situations are routed to the applicable instructions and professional review.
What engineering checks establish
Deterministic tests exercise reference cases, rounding behavior, invalid inputs and conservation of basis. They check that taxable and tax-free conversion components reconcile, that recovered basis does not exceed the available amount, and that unsupported scenarios do not receive an ordinary definitive result. Browser checks cover interactive controls, saved-scenario reuse, imports, exports, links, responsive layout and accessibility. The same inputs should lead to the same supported result without depending on a remote financial service.
Those checks establish behavior for the tested cases. They cannot establish that every visitor entered a complete IRA inventory, that an administrator approved a transaction or that tax law has no exception relevant to a particular person. The site therefore distinguishes a numerical model, a transaction-eligibility question and a filing instruction. A worksheet can show explanatory allocation rows even when the official form follows a shorter Part I or Part II branch. Readers should keep that distinction when transferring information into preparation software.
Local tools and financial privacy
The calculators perform their arithmetic in browser JavaScript. The application does not submit entered IRA balances or basis figures to a financial-input API. Optional saving uses the browser's local storage and is not an encrypted online account. Reset and clear controls remove the applicable local records, while downloaded worksheets remain under the user's control. The privacy policy explains ordinary hosting requests, contact email and the separate advertising-cookie disclosures in more detail.
Local-first design does not make a shared device private or turn browser storage into a durable backup. Someone using the same profile may be able to view saved records, and deleting a browser record does not erase a file already exported or an email already sent. The website does not need account credentials or identifying tax documents to explain a fabricated example. Keep sensitive records in an appropriate personal system and share them only through a channel suitable for professional financial or tax work.
How to use the site responsibly
Begin with the guide library if the contribution/conversion distinction is unfamiliar, or use the reference encyclopedia for a particular term. Gather prior Forms 8606 and year-end account statements before entering numbers. Test one changed assumption at a time, read the warnings and record any unresolved facts. A reverse-rollover projection should be accompanied by receiving-plan confirmation, not treated as instructions to transfer all IRA money. A complete return projection may be needed for benefits, credits, state taxes or substantial bracket effects.
If an explanation appears inconsistent with an IRS source, send the page address, tax year, fabricated inputs and the source passage through Contact. The maintainer reviews useful reports and updates the publication when a correction is warranted. Check the page date and source year when revisiting an older example. The goal is a useful, inspectable planning reference that helps readers ask better questions and preserve better records, without claiming to provide individualized tax, legal, accounting or investment advice.