V4 and V5 scores

From the November 2026 edition, the Silktide Index gives every website two accessibility scores. The V4 score is calculated the way Index scores have been calculated for years. The V5 score is calculated the way the latest version of Silktide scores accessibility. You can switch between them on the Index's accessibility pages.

Both scores come from the same test. Each month we test a sample of up to 125 pages from each website (25 for most websites, as in every edition since 2023), and the PDFs we find, with the same automated accessibility checks, against 2.2. The two scores apply different rules to the same results.

Neither score is more correct than the other. Each is consistent with itself, so compare a website's V4 score with other V4 scores, and its V5 score with other V5 scores.

What both scores have in common

The scale. Both run from 0 to 100, where 100 means we found no problems our checks can detect.
The checks. Both use the same set of automated checks, run on the same pages. Checks that only prompt a person to take a look, because a machine cannot judge them, are never scored.
Each check scores the whole website. A check's result blends how many of the tested pages are affected with how many issues each affected page has. One issue on one page costs far less than the same issue on every page.
Level scores. Both show a score for each : A, AA and AAA.
No decisions. The Index tests every website as a first-time visitor sees it. Decisions an organization has made in its own Silktide account, such as marking an issue as a false positive, are never applied.

How the V4 score is calculated

The V4 score is built from a tree of categories. Each WCAG level, A, AA and AAA, is a category, and so is mobile accessibility. Each category scores the checks inside it, each check with an impact fixed for that category, and the categories combine into the overall score by weight:

Category	Weight
Level A	45
Level AA	40
Level AAA	15
Mobile	10

Each level score is the score of that level's own checks, so a website can score higher at AA than at A. PDFs count toward the V4 score alongside pages.

These rules have not changed in the November 2026 edition. A V4 score can still move from one month to the next when the website changes, when different pages are tested, or when one of our checks is fixed. See What changed in the November 2026 Index.

How the V5 score is calculated

The V5 score starts at 100, and each check takes off up to a fixed number of points, called its impact, depending on how badly the website fails it:

points taken off = impact x (100 - check score) / 100

A check with an impact of 10 that scores 70 takes off 3 points. A check the website passes takes off nothing.

Where impacts come from. The most important checks keep the impact they had in V4, so the problems that mattered most before still matter most. Every other check's impact comes from its priority and how confident the check is that it has found a real problem.
Every level counts toward one score. Checks at levels A, AA and AAA are pooled into one score. A check counts once, however many levels it belongs to.
Level scores include the levels below them. The AA score covers the level A and AA checks, and the AAA score covers all three, exactly as WCAG conformance works. A website's AA score can never be higher than its A score.
Web pages only, for now. V5 scores PDFs with a newer, more detailed set of PDF checks that the Index does not run, so the Index's V5 score covers web pages only. PDFs still count toward the V4 score.

The full method, with a worked example, is in How scoring changed in Silktide 5. It describes Silktide accounts, which run more checks than the Index, but every rule on that page applies to the Index's V5 score.

How the two differ

	V4	V5
How points are counted	Category by category, then combined by weight	One pool of checks, each taking off up to its impact
Impacts	Fixed by Silktide for each check in each category	V4's impacts for the most important checks; priority and confidence for the rest
Level scores	Each level scored on its own checks	Each level includes the levels below it
PDFs	Counted alongside pages	Not counted yet
History	Every edition of the Index	From the November 2026 edition

Because they weigh the same problems differently, the same website can score higher in V4 than in V5, or the other way around, and can rank differently in each.

Why a website can have a V4 score but no V5 score

Both scores come from the same test, so almost every website that has one has the other. A website can have a V4 score without a V5 score when its V5 score was not recorded for that test. It is then left out of the V5 rankings for that month, rather than shown as scoring 0, and appears again after its next test.

Why your Silktide account scores differently

If your organization uses Silktide, your account's accessibility score for a website will usually differ from its Index score, in both V4 and V5:

Your account tests more pages. The Index tests a sample of up to 125 pages, and 25 for most websites. Your account tests the pages it is set up to test, often your whole website.
Your account runs more checks. Silktide accounts also run newer checks, for , accessibility best practices, more WCAG success criteria, and PDFs against . These are not part of the Index.
Your account applies your decisions. Issues your team has marked as false positives, or approved, no longer count against you there. The Index never applies them.

V4 is being retired

The Index shows V4 and V5 side by side for now, so that you can keep comparing with earlier editions. We plan to retire V4 scores in 2027, and we will announce when well before it happens.

What changed in the November 2026 Index - why scores moved between the October and November editions.
How scoring changed in Silktide 5 - the V5 scoring method in full.