Your Portfolio Captured 80% of the IHSG's Gains and 95% of Its Losses. Here's Your Upside and Downside Capture Ratio
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5 min read
Indonesia's stock market had a brutal first half of 2026. IHSG, the Jakarta Composite Index, fell in every single month from January through June, a cumulative loss of about 35% (Bloombergtechnoz, 30 June 2026). Then it flipped hard: up 10.28% in July alone, then another 4.52% in August (CNBC Indonesia; Liputan6).
If you held a diversified portfolio through that stretch, two separate questions matter. How much of the six-month fall did your portfolio dodge? And how much of the two-month rebound did it actually get in on? Those are two different numbers, and together they have a name: upside and downside capture ratio.
Upside capture ratio asks: in the months a benchmark went up, how much of that gain did your portfolio also get? Downside capture ratio asks the mirror question: in the months the benchmark went down, how much of that loss did your portfolio also take?
Both are expressed as a percentage of the benchmark's own move. A downside capture of 60% means that when the benchmark fell 10%, this portfolio only fell about 6%. A downside capture of 95% means it fell almost exactly as much as the benchmark did, offering barely any protection at all.
The calculation splits a benchmark's history into two buckets: months it was up, and months it was down. Then it compares the portfolio's average return in each bucket to the benchmark's average return in that same bucket.
(Average portfolio return in that bucket ÷ Average benchmark return in that bucket) × 100
Some fund databases use a compounded, cumulative version of the same idea instead of a simple average, which will land on a very close but not always identical number. The concept is the same either way: what share of the benchmark's move, in each direction, actually showed up in the portfolio.
Here is IHSG's actual monthly performance for the first eight months of 2026, alongside a hypothetical Fund A built to illustrate the mechanic.
| Month | IHSG (real) | Fund A (illustrative) |
|---|---|---|
| Jan 2026 | -3.67% | -3.49% |
| Feb 2026 | -1.13% | -1.07% |
| Mar 2026 | -14.42% | -13.70% |
| Apr 2026 | -1.30% | -1.24% |
| May 2026 | -11.92% | -11.32% |
| Jun 2026 | -7.90% | -7.51% |
| Jul 2026 | +10.28% | +8.22% |
| Aug 2026 | +4.52% | +3.62% |
Averaging the six down months, IHSG lost about 6.72% a month and Fund A lost about 6.39% a month: 6.39 ÷ 6.72 = a downside capture ratio of roughly 95%. Averaging the two up months, IHSG gained about 7.40% a month and Fund A gained about 5.92% a month: 5.92 ÷ 7.40 = an upside capture ratio of exactly 80%.
Fund A gave up a fifth of IHSG's rebound while still absorbing 95% of its crash. On a headline number like annual return, Fund A might look like a reasonably close tracker of the index. This pair of ratios shows the asymmetry a single return figure hides.
Beta measures one thing: how much a portfolio tends to move relative to a benchmark, on average, across all months, up and down together, compressed into a single number. A beta of 0.9 sounds like a modest, defensive tilt. It says nothing about whether that 0.9 comes from capturing 90% of both directions evenly, or from Fund A's 80/95 split above, where the shape of that same rough average is quietly stacked against you.
Capture ratio splits the up months and down months apart on purpose, because that asymmetry is exactly the thing an all-months average erodes.
NetWort's Portfolio Health section on your dashboard already calculates your real portfolio beta and real maximum drawdown from your actual holdings, not a hypothetical one. Capture ratio itself isn't a separate labeled number there today, but those two figures point at the same underlying question this article walks through: does your portfolio's shape work for you on the way down as well as the way up? Pull up your own beta and drawdown numbers on the dashboard, and compare them against how the market you're benchmarked to, IHSG for IDX-heavy portfolios, actually moved over the same stretch on the market page.