IHSG Return in Dollar vs Rupiah: Why the Same Index Move Tells Two Different Stories
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5 min read
If you are an Indonesian investor tracking the IHSG in rupiah, 2026 already looks bad: the index is down about 26.6% since the end of 2025. If you are a foreign investor holding the same index, priced in dollars, the number you actually lived through was worse. Closer to 31%.
Same index. Same two dates. A five-percentage-point gap that has nothing to do with which stocks the index holds.
The Jakarta Composite Index (IHSG) is quoted in rupiah. That is the number an Indonesian investor sees and the number every headline reports. A foreign investor, though, does not care what the index did in rupiah. They care what happened to their own money, and their money started as dollars, got converted to rupiah to buy Indonesian shares, and eventually has to convert back.
That round trip adds a second return on top of the index's own move: whatever the rupiah did against the dollar in between.
Return in USD = (1 + Return in IDR) × (IDR/USD at start ÷ IDR/USD at end) − 1
When the rupiah weakens while the index is also falling, both effects point the same way and the dollar loss ends up larger than the rupiah loss. That is exactly what happened this year.
The IHSG closed 2025 at 8,646.94 points (30 December 2025, Antara News) and closed at 6,351.13 points on 5 August 2026 (Kompas.com), a fall of about 26.6% in rupiah terms.
Over roughly the same stretch, the rupiah itself weakened against the dollar: from Rp 16,788 per US dollar at the close of 29 December 2025 (Investor.id, citing Bloomberg data) to Rp 17,919 per US dollar on 6 August 2026, Bank Indonesia's JISDOR reference rate. That is the rupiah losing about 6.7% of its dollar value over the same window.
| Rupiah investor | Dollar investor | |
|---|---|---|
| IHSG, late Dec 2025 | 8,646.94 | 8,646.94 |
| USD/IDR, same date | not applicable | Rp 16,788 |
| IHSG, early Aug 2026 | 6,351.13 | 6,351.13 |
| USD/IDR, same date | not applicable | Rp 17,919 |
| Return over the period | −26.6% | −31.2% |
The IHSG dates and the USD/IDR dates are one trading day apart at each end (30 Dec vs 29 Dec, 5 Aug vs 6 Aug) because a confirmed same-day close was not available for both series on the exact same days. The gap is small enough that it does not change the story: a dollar-based investor lost close to five percentage points more than the rupiah figure alone suggests.
Say a foreign investor converted $10,000 into rupiah on 29 December 2025, at Rp 16,788 per dollar, giving them Rp 167,880,000 to put into an IHSG-tracking position.
If that position moved exactly with the index, −26.6%, it would be worth about Rp 123,270,000 by 6 August 2026. Converting that back to dollars at the day's JISDOR rate of Rp 17,919 gives roughly $6,880, a loss of about 31.2% on the original $10,000. The rupiah return and the dollar return describe the same investment, but they are not the same number, and the difference is entirely the exchange rate.
This is not an unusual quirk. 2026 has been a genuinely difficult year for the rupiah, not just for Indonesian stocks. A widening balance-of-payments deficit, an oil price shock tied to Middle East tensions, and a run of Bank Indonesia rate hikes to defend the currency all pushed USD/IDR to record weakness earlier in the year. The correlation between the dollar's global strength and the IHSG has been unusually tight through this stretch precisely because both are being driven by the same domestic pressure, not by coincidence.
That matters for anyone comparing an Indonesian portfolio's performance to a foreign one: the currency is not a rounding error sitting on top of the "real" return. In a year like 2026, it has been a bigger swing factor than most individual stock picks.
The direction of this effect flips depending on which way the money is moving. An Indonesian investor holding US stocks has been seeing the opposite: a weaker rupiah has been inflating their rupiah-denominated returns on holdings that, in dollar terms, barely moved. Same mechanism, opposite direction, depending on which currency you started in and which one you are measuring against.
If you hold any foreign-currency assets, whether that is IHSG exposure held from abroad or US holdings measured in rupiah, your headline return alone will not tell you how much of it came from the market and how much came from the exchange rate. Open the FX Exposure view on your NetWort dashboard to see your own currency breakdown, and check the Macro page for the current USD/IDR level before comparing any return across currencies. A return that looks strong, or weak, in one currency can tell a materially different story once the exchange rate is separated out.