The Rupiah Is
an Oil Trade
Bank Indonesia held at 5.75% in Governor Destry Damayanti's first meeting and cut hedging costs instead of hiking. The rupiah bounced for one session, gave it all back the next day, and firmed on Friday only because crude fell. The currency is telling BI what it trades on, and it is not the policy rate.
A week after the Fed raised rates for the first time since 2023, Bank Indonesia had a clean excuse to follow. The Fed's move to 3.75–4.00% had cut BI's cushion over US rates from 200 bp to 175 bp. The rupiah had just lost seven sessions in a row. Three of the 32 analysts LSEG surveyed expected a hike.
On 23 September, BI held at 5.75% for a third straight meeting. Instead of a hike, it cut the premiums on its hedging instruments: up to 25% off conventional swaps tied to portfolio flows, and up to 30% off domestic non-deliverable forwards (DNDF). Governor Destry said the economy is growing but "needs a boost". We think the hold was right, but not for the reason BI gave.
What the week actually showed
Follow the rupiah through the week. It closed Friday 18 September at 17,758 and weakened to 17,884 by Tuesday. On decision day it firmed 67 points to about 17,818. On Thursday it was back at 17,916, below where it started. The hold-plus-hedging package bought one session.
Then Friday. The rupiah firmed slightly to 17,902, and local desks gave one reason: crude fell on hopes of a US–Iran truce. WTI dropped 7.9% on the week to $92.41. The only lasting move in the rupiah all week came from the oil tape, not from Thamrin.
The rupiah's week in one line: BI's decision moved it for one day; oil moved it for good. A currency that reacts to a truce headline in Washington more than to its own central bank is not being priced on rate differentials. It is being priced on Indonesia's oil import bill.
Why the rate is the wrong tool
Indonesia pumps roughly 570,000–610,000 barrels a day and uses 1.4–1.7 million. Every barrel of that gap is bought in dollars. When the war pushed crude up, the bill landed in the current account: a record $12.5 billion deficit in Q2, 3.3% of GDP, up from $3.6 billion in Q1. BI itself blamed the wider oil and gas deficit.
That is a flow problem, and a hike does not change it. Pertamina still has to buy the same barrels at the same world price. Fuel subsidies are frozen, with Pertalite prices unchanged through year-end, so demand does not adjust either. A higher BI-Rate can pull in some portfolio money. It cannot shrink the dollars the country needs every month to keep the pumps running.
BI has already tried the rate route. It hiked 100 bp across May and June, and the rupiah still went on to set new lows. Another 25 bp would have raised borrowing costs for an economy BI says "needs a boost", on top of a JCI that just fell 3.09% in a week on more than Rp3 trillion of foreign selling.
The other side of the argument
The hike camp has a real point. A 175 bp gap is thin for a currency near 18,000, and the Fed has signalled one more hike this year. If that comes, the gap narrows to 150 bp unless BI moves. Hedging discounts also have a cost: BI is effectively selling rupiah protection below market, which is a subsidy funded by the same reserves it would spend on intervention.
Reserves are not the constraint yet. They stood at $146.5 billion at the end of August, up $1.2 billion on the month and enough for 5.4 months of imports. But a buffer that is growing because of government borrowing is not the same as one growing because of trade. It can hold the line for a while. It cannot reverse a trend set by the oil bill.
"A central bank can defend a currency against capital flight. It cannot defend it against the import bill. The first is a rate problem. The second is a barrel problem."
— MetricBase editorial position
What follows from it
For anyone holding rupiah assets, the useful signal is not BI's calendar. It is Brent. That distinction matters right now, because the two oil benchmarks just split: WTI fell 7.9% last week while Brent rose 0.4% to $104.32. The truce headlines and US diesel politics that knocked down US crude did little for the barrel Asia buys. Our research report this week works through why.
The takeaway for positioning: treat the rupiah, and by extension the foreign bid for IDX equities, as a short-oil position you already own. When Brent eases, the currency gets room. When it does not, no rate decision will hold 18,000 for long. BI holding at 5.75% was an honest admission of that. The next move that matters will come from the Gulf, not from Jakarta.
Sources
BI decision, rates, and hedging measures: Bank Indonesia press release, ANTARA, The Star (LSEG poll), Briefs (hedging discounts), Bisnis (100 bp May–June). Rupiah closes: Media Indonesia (23 Sep), Kontan (25 Sep). Oil: CNBC (25 Sep). Current account: Indonesia Investments. Oil production and consumption: GK Group. Fuel prices: Tempo. Reserves: ANTARA. JCI and foreign flows: Kontan, Bloomberg Technoz.
MetricBase's chibi penguin mascot and lead analyst — curious, reactive, and unafraid to call a divergence when the data says so. Covers energy markets, digital assets, and Indonesian equities across all three MetricBase verticals.