Methodology

Where index valuations come from

NSE publishes a daily snapshot of every index it maintains, including price to earnings, price to book and dividend yield. We read that file once per trading day, keep the original verbatim, and load it unchanged — we do not recompute PE from constituents, so the numbers here are the numbers NSE published.

History comes from three NSE sources, kept separate on purpose because they do not begin on the same day:

• Valuation ratios from 1 January 1999. NSE's historical PE / PB / dividend-yield report. This is the earliest PE that exists at the source — there is no ratio data before it, and none can be inferred.
• Index levels from 3 August 1990. A separate NSE report carrying only the closing level. Values before November 1995 are NSE's own back-cast: the Nifty 50's real base date is 3 November 1995, when it was set to 1000.
• The daily snapshot from March 2012. One file per trading day covering every index, which is what the site reads each evening.

So a chart can show an index level back to 1990 while its PE only starts in 1999. That gap is real and we do not paper over it by back-computing earnings that were never published.

Where the sources overlap they agree exactly — we checked every trading day of 2013, 2020 and 2026 against the snapshot archive and found no disagreement — so the joins are seams in provenance, not in the numbers. Each index starts at its own inception; only the older ones reach back to 1999.

The March 2021 methodology change

On 2021-03-31 NSE moved index earnings from standalone to consolidated accounts. Consolidated earnings are generally higher, so published PE stepped down — not because the market got cheaper, but because the denominator changed.

We do not splice the two series together or adjust one to match the other; both would be guesswork presented as fact. Instead the change is marked on every chart, and every index page offers a since Mar 2021 window that compares like with like. A percentile over the full history spans both methodologies, and that is worth knowing when you read it.

How percentiles are computed

The bands are the 10th, 25th, 50th, 75th and 90th percentiles of the index's own daily closing values across the chosen window, computed with linear interpolation. The percentile rank is the share of trading days in that window at or below today's value.

Windows are calendar windows counted back from the most recent trading day, not fixed counts of observations. Below 60 observations we show the raw value and no percentile: a percentile over a handful of days is not a percentile.

What we do not do

• We publish valuation data and rankings. We do not make buy or sell recommendations, rate securities, or offer investment advice of any kind.
• A low percentile is not a signal. Indices can stay cheap for years, and an index can be cheap precisely because its earnings are about to fall.
• We do not silently drop data. An index we cannot match to a name is recorded as an open issue rather than omitted, and gaps in history stay visible as gaps.

Sources

• Index PE, PB and dividend yield — NSE daily index snapshot, via niftyindices.com.

All data is end of day. We fetch once per trading day and cache aggressively, both to serve pages quickly and to stay a light load on the sources.