Today's 50 stocks returned 16.2% a year since 2016; the real index stocks returned 12.8%.
Most backtesting tools and tutorials start the same way: download the stocks in the NIFTY 50 today, and test a strategy on them over the last ten years. It sounds harmless. It isn’t, because today’s list is a list of survivors. Stocks get into the NIFTY 50 by rising; they leave it by falling. A backtest on today’s 50 has been told the winners in advance.
To measure how much that matters, we ran the simplest possible portfolio on two versions of the index, from January 2016 to August 2026: an equal-weight buy-and-hold of every stock in the universe, rebalanced daily.
- The real NIFTY 50: on each day, only the stocks that were in the index that day.
- Today’s NIFTY 50: the 50 current members, back-tested over the whole period (each from the day our data starts for it).
Weekly values. The official index is cap-weighted and excludes dividends, so it is shown for reference only. Hover or tap for values.
₹1 lakh grows to about ₹3.6 lakh on the real index stocks, but to ₹4.9 lakh on today’s list. The gap opens in almost every year, and the biggest gaps come in years when the eventual winners were still small: in 2018 the real index stocks lost 6.1% while today’s list made 1.2%, and in 2019 the gap was 8 points (3.0% against 11.0%).
Where the phantom return comes from
Stocks enter the index after they’ve already gone up. Here are the current members that joined after 2016, and how much each rose in the two years before it was added. A backtest on today’s list owns all of that rise; the real index owned none of it.
| Stock | Joined the NIFTY 50 | Price change in the 2 years before joining |
|---|---|---|
| TRENT | 2024-09-30 | +159% |
| BAJFINANCE | 2017-09-29 | +111% |
| ADANIENT | 2022-09-30 | +101% |
| BEL | 2024-09-30 | +58% |
| JSWSTEEL | 2018-09-28 | +52% |
| NESTLEIND | 2019-09-27 | +26% |
| INDIGO | 2025-09-30 | +21% |
| HDFCLIFE | 2020-07-31 | +1% |
| MAXHEALTH | 2025-09-30 | −3% |
| SBILIFE | 2020-09-25 | −19% |
The other half is the stocks that are missing. 29 stocks were in the index at some point since 2016 and aren’t today, including YES Bank, Zee Entertainment, Vedanta, IndusInd Bank and BPCL. Several left after large falls. A backtest on today’s list never holds them, so it never takes those losses.
| Year | Real NIFTY 50 | Today’s 50 | Difference |
|---|---|---|---|
| 2016 | 8.7% | 10.7% | +1.9 pts |
| 2017 | 26.9% | 31.3% | +4.5 pts |
| 2018 | −6.1% | 1.2% | +7.3 pts |
| 2019 | 3.0% | 11.0% | +8.0 pts |
| 2020 | 19.4% | 22.9% | +3.5 pts |
| 2021 | 33.9% | 37.7% | +3.9 pts |
| 2022 | 6.1% | 8.3% | +2.2 pts |
| 2023 | 29.6% | 29.9% | +0.3 pts |
| 2024 | 10.2% | 15.2% | +4.9 pts |
| 2025 | 13.3% | 12.2% | −1.1 pts |
| 2026 (to Aug) | −1.5% | −1.5% | +0.0 pts |
A bonus finding: the gains came overnight
The same data shows something most intraday traders don’t expect. On the real index, the average stock fell 8.1 bps between the open and the close of a typical day, even though the stocks gained 12.8% a year overall. The decade’s gains came between one day’s close and the next day’s open. Buying at the open and selling at the close, every day, would have lost money before any costs.
Prices are back-adjusted for splits and bonuses but exclude dividends. Three former members have no minute data in our snapshot (HDFC Ltd, Cairn India, Tata Motors DVR), so the real-index portfolio is one to three stocks short on some days. Two of them left through mergers (HDFC Ltd into HDFC Bank, Cairn India into Vedanta), so their effect on the comparison is likely small.
What to take from this
- Always test on the stocks that were in the universe on each day. A “today’s list” backtest adds about 3.4% a year here, before any strategy is involved.
- The bias is biggest for long holding periods and momentum ideas, because the winners are exactly the stocks that rose before joining.
- Every DataPointX result uses point-in-time membership. It’s built into dpx_bt and can’t be switched off.
Have a variation in mind?
Ask runs your own idea on the same data and rules, with the same report: net after costs, +3 bps stress test, three periods.
Backtest on historical data (Jan 2016 – Aug 2026), net of discount-broker (₹20 per order) and statutory charges and 1 bp slippage per fill. Education and research only, not investment advice. Past results do not predict future returns. Disclaimer.