Turn on the evening news and you'll hear it: "The Colombo bourse closed higher today, with the ASPI gaining half a percent." For most people it washes over them. But once you understand what the ASPI is, that one number becomes a useful daily read on the whole market. Here's the plain-language version.
In one line: the ASPI — the All Share Price Index — is a single number that summarises the price movement of every company listed on the Colombo Stock Exchange. When it rises, the market as a whole is worth more than it was; when it falls, less. It's the market's daily temperature reading.
What an index actually is
An index is just a weighted average of many share prices rolled into one figure, so you can track "the market" without watching hundreds of individual stocks. Instead of asking "how did all 280-odd listed companies do today?", you glance at one number.
The ASPI is market-capitalisation weighted. That's an important detail: bigger companies move the index more than smaller ones. A company worth Rs. 500 billion has far more pull on the ASPI than one worth Rs. 2 billion. So when you hear the ASPI moved, it's mostly telling you what happened to the large companies.
ASPI vs. S&P SL20 — the two you'll hear about
Sri Lanka has two headline indices, and it helps to know the difference:
The two main indices
- ASPI (All Share Price Index) — covers every listed company. The broadest measure of the whole market.
- S&P SL20 — tracks only the 20 largest and most liquid companies. A cleaner read on the big, heavily-traded names.
If the ASPI is the whole classroom's average, the S&P SL20 is the average of just the front row — the biggest, most actively traded students.
What the ASPI does not tell you
This is where careful investors part ways with casual watchers. The ASPI has real limitations:
- It's a price index, not a total-return index. It tracks share prices only — it does not include the dividends companies pay. Since dividends are a big part of long-term returns in Sri Lanka, the ASPI actually understates what a long-term investor earned.
- It's dominated by a few giants. Because it's market-cap weighted, a handful of very large companies can push the index around even if most other stocks did nothing — or the opposite.
- *A rising index doesn't mean your stock rose.* The market can be up while the specific company you own is down, and vice versa.
The ASPI tells you what the market did. It tells you nothing about whether you made a good decision.
So how should an investor use it?
The ASPI is context, not a signal. Sensible ways to use it:
- As a benchmark. Over a year, did your portfolio beat the ASPI or lag it? That's a fair scoreboard for how your picks did versus simply "the market."
- As a sentiment gauge. A market falling hard for weeks tells you fear is high — which can mean bargains are appearing for the patient.
- As a reality check. If your stock soared while the whole market soared, some of that was the tide, not your genius. If it rose while the market fell, that's more likely the company itself.
What the ASPI should not be is a reason to buy or sell. "The index is up, so I'll buy" is not a strategy — it's following a crowd whose reasons you don't know.
A note on the number itself
The ASPI is set against a historical base value, so the absolute figure (whether it's 10,000 or 12,000) only means something relative to the past. What matters isn't the level — it's the change and the trend. Don't anchor on the raw number; watch the direction.
The bottom line
The ASPI is a brilliant summary and a poor instruction. Understand it, glance at it daily for context, use it to benchmark yourself honestly — and then make your actual decisions the same way you always should: one business at a time.