How we build and check our calculators

Four rules we hold ourselves to

LoopNode tools answer questions where a wrong number costs people money or plans: whether a car loan’s interest is deductible, when someone can retire. This page explains how we build and check them, and where the checks differ from one tool to another — so you can judge how far to trust a result.

1. Only primary sources. A rule goes into a tool only if we can quote it from the government page, law or regulation that sets it.
2. Show the working. Every result comes with its steps and the source of each rule, so you can check it against your own documents.
3. Leave out what we cannot verify. If no primary text states a rule, the tool says so instead of guessing.
4. Fix mistakes in the open. Confirmed errors are corrected and listed below, and the serious ones get a test that would have caught them.

1 · Primary sources, with dates

Each tool keeps its rules in a data file, separate from the code, with the exact passage each rule comes from, quoted in the original language. In the retirement calculator’s file, every rule also carries the address of its page and the date we read it, and we keep a saved copy of each page. The car checker’s file names its source — the Treasury regulation — and the date we read it once, for the whole file.

The retirement calculator’s file holds 68 quoted passages from GOSI’s pages and from the text of the 1445 AH Social Insurance Law, including every row of both transition tables [1][2]. An automated test checks that each of the 68 still appears, word for word, in the saved copy of its page. The car checker’s file quotes the Treasury regulation section by section: 19 rules, and 8 of the 19 worked examples the regulation contains [3].

“Leave out what we cannot verify” is not a slogan. The retirement calculator did not show the new law’s early-retirement discount until we found the law’s own text on 30 September 2026 [2]. Until then, the page said the rate was not shown and why. It now states the rate, but it does not calculate the reduced amount yet.

2 · An answer key worked out by hand

For each tool we work out a set of cases by hand from the sources, including the examples the agencies publish themselves. For the retirement calculator that is eight cases covering every group and the traps: GOSI’s own pension example and its early-retirement example (215 months, so 324 needed), plus our own cases for two people born a day apart, for periods already compensated, and for the 100% cap. For the car checker it is 8 of the regulation’s worked examples plus eight real VINs whose plants and weight classes we checked.

A tool is only finished when it reproduces every number in its key exactly. The key then stays in the test suite, so a later change that breaks one of them cannot ship.

3 · A second calculator, for the retirement tool

Hand-made cases catch the obvious; they do not catch every edge. For the retirement calculator, a separate AI review wrote a second, throwaway calculator from the sources — an “oracle” — and ran both on the same inputs. We have used an oracle only for the retirement calculator; the car checker is tested against the regulation’s examples and real VINs instead.

Those figures come from the review of 30 September 2026, in our internal records. The cases covered every age band, both sides of each boundary, 29 February births and 1,500 random people. The consistency checks test properties that must always hold, whatever the rules: more months of contribution never make your retirement later, a later birth never makes it earlier, and the pension never falls when your wage rises. The same review found that new-law pensions could go above the 100% cap and be paid below 180 months; since the fixes of 30 September 2026, the pension never breaks its cap or its minimum.

4 · A red team that tries to break it

Each site also goes through a red-team review, run apart from the build, whose only job is to make the tool give a wrong or misleading answer. It types Arabic-Indic digits, pastes numbers with invisible characters, chooses impossible dates, switches off JavaScript, prints the page, shrinks it to a 280-pixel phone, and simulates the outside services failing.

In the review of 30 September 2026, the car checker was tested with 16 real lookups to NHTSA’s decoder, and every kind of failure of that service was simulated. A crawl of the sites followed 96 addresses across 12 pages and found no broken links. Both figures are from our internal records. Each must-fix finding became a test that failed first and passed only once it was fixed; the fixes are in the corrections log below.

5 · Checks before release

• Accessibility. An automated audit on every page, plus our own colour-contrast check, because the standard audit skips Arabic text.
• Phones. No page may scroll sideways on phone-width screens, in light or dark mode — tested down to 320 pixels wide, and to 280 on this site and the retirement calculator.
• Speed and stability. Releases that change a page’s layout, text or scripts are measured for load speed and layout shift on every page.
• Reproducible builds. For this site and the retirement calculator, two builds from a clean copy must produce byte-identical files, so what we tested is exactly what is published.

Nothing you type leaves your browser

The retirement calculator does all of its arithmetic on your device. A test types a full set of details and checks that no request leaves the site — its fonts load from the same site — and that nothing is stored. The car checker sends one thing, the VIN, and only when you ask for a check: straight to NHTSA’s public decoder, not to us [4]. Your loan figures and income stay in your browser. Neither tool has accounts or a database. The privacy policy has the details.

LoopNode is independent. We are not affiliated with the IRS, the Treasury Department, NHTSA or GOSI, and our results are estimates to help you understand the rules. They are not tax, legal or financial advice.

Corrections log

Confirmed errors, what we changed, and when. The first entries come from the separate AI review of 30 September 2026; the newest from the fact-check of these guides on the same day.

• 30 Sep 2026 Guides Fact-check of the five guides: the new law covers everyone with no uncompensated earlier periods, including people whose earlier periods were all paid out as compensation. The Saudi guides and the retirement calculator had said “no contribution periods at all”; its form now asks about uncompensated periods.
• 30 Sep 2026 Guides Saudi early retirement: the 324 months in GOSI’s example apply in each system separately, 180 months is the minimum for a retirement pension, and the implementing regulation is cited.
• 30 Sep 2026 Guides Car loan interest: model year does not make a car used; a car that someone else already owned, titled or leased does. The VIN guide now says that motorcycles and trucks or vans rated over 8,500 pounds may have no assembly label.
• 30 Sep 2026 Guides This page: the car regulation has 19 worked examples, of which our file holds 8; the second “oracle” calculator was used only for the retirement calculator; GOSI publishes one early-retirement example, not two.
• 30 Sep 2026 Retirement calculator New-law pensions: a pension now needs at least 180 months, is capped at 100% of the average wage, and is raised to the Article 17 minimum (2,000 to 4,000 riyals). Before, 12 months showed a small monthly pension.
• 30 Sep 2026 Retirement calculator A birth date after 3 July 2024 with earlier contribution periods now gives a clear error; before, the page stopped responding and could leave an old result on screen.
• 30 Sep 2026 Retirement calculator Numbers are no longer cut off silently (“215” typed as years became 21), and impossible combinations — more months than a person could have worked — are flagged.
• 30 Sep 2026 Retirement calculator The page now states the new law’s early-retirement discount from the law’s text (3% for every 12 months).
• 30 Sep 2026 Car checker Refinancing: the original loan must itself have been taken after December 31, 2024; the checker now asks.
• 30 Sep 2026 Car checker A weight rating typed from the door label is checked against NHTSA’s weight class, and a vehicle that does not qualify never shows a deduction amount.
• 30 Sep 2026 Car checker A VIN whose check digit does not match is never marked as qualifying, and a 2023-or-older model year gets a reminder that only new vehicles qualify.
• 30 Sep 2026 LoopNode home The example VIN in the showcase is now a 2026, US-built vehicle; the earlier 2003 VIN could not qualify.

Found something we got wrong? Tell us what you entered, what the tool showed and what you expected, with a link to the official source if you have one.

This page describes how we build and test our tools; it is not tax, legal or financial advice.