72(t) Accuracy Check: Dinkytown and calcxml Against the IRS
Dinkytown and calcxml are the two free 72(t) tools people asking about a SEPP plan get pointed to most. We ran the IRS's own worked examples through both. Each gets fixed amortization and the required minimum distribution method exactly right. Each is wrong on fixed annuitization, by the same amount, on the same example.
What the same $400,000 pays under each method
$400,000 IRA, age 50, 4% interest rate, Single Life Table, factor 36.2 — the IRS's own worked examples. "This site" is computed live by the engine on this page, the same one checked against all ten examples on the test cases page; it is not a fixed number typed into this page.
| Method | IRS's own example | This site | Dinkytown | calcxml |
|---|---|---|---|---|
| Fixed amortization IRS SEPP FAQ Q&A 7, example 2 | $21,102 | ✓ $21,102 | ✓ $21,101.63 | ✓ $21,102 |
| RMD, year one IRS SEPP FAQ Q&A 7, example 1 | $11,050 | ✓ $11,050 | ✓ $11,049.72 | ✓ $11,050 |
| Fixed annuitization IRS SEPP FAQ Q&A 7, example 3 | $22,030 | ✓ $22,030 | ✗ $20,880.34 | ✗ $20,880 |
Dinkytown's amortization and RMD figures land a few cents from the IRS's rounded dollar because of intermediate rounding in the annuity factor — both round to the same whole dollar the IRS publishes, which is not an error. The annuitization gap is not rounding: $1,150 a year, 5.2% of the correct figure, and it repeats to the dollar on both tools.
Why annuitization specifically
Notice 2022-6 s 3.01(c) prices fixed annuitization off the mortality rates in 26 CFR § 1.401(a)(9)-9(e) Table 4, not a life expectancy table. Applying a life-expectancy-style table to this one method instead is, in the IRS's own description of common errors, the single most common implementation mistake — the test cases page named this exact failure mode before we had two real examples of it. We have not seen either tool's source, so we cannot say which table each one actually reads; we can say both land on the same wrong number, to the dollar, which is consistent with both reaching for the wrong table rather than two independent errors that happened to agree.
Check it yourself
Enter $400,000, age 50, 4%, Single Life Table into either tool. Fixed amortization should read $21,102 and the RMD method $11,050. Switch to fixed annuitization: the answer is $22,030. If a tool gives you $20,880 instead, it is reading the wrong table for that one method, and every later year built on it is wrong by the same proportion.
How this was tested, and when
Tested by hand in a browser on 9 September 2026, entering the inputs above directly into each tool's own form and reading its own output — not estimated, not taken from a review. Dinkytown at dinkytown.net/java/72t-calculator.html, calcxml at calcxml.com/calculators/72t. Both are otherwise capable, widely used tools; this is one specific, narrow, checkable disagreement on one method, not a claim that either is broadly unreliable. Both are free to fix it, and this page is dated so a future visitor can tell if they have. If you get a different result testing either tool today, or if this page itself is ever wrong against the IRS's examples, write to hello@savingslast.com; it goes in the corrections log.
Printed from https://savingslast.com/72t-accuracy-check/ on . The figures reflect the inputs shown and the rules as published on that date.