The Uninvested Cash Sitting in Your Brokerage App Is Quietly Dragging Down Your Return
5 min read
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5 min read
You sell a stock, or you top up your account, and the cash sits there for a few weeks while you decide what to buy next. That cash is parked in your RDN, short for Rekening Dana Nasabah, the bank account your securities firm uses to hold your uninvested funds. It barely earns anything while it waits. Meanwhile the rest of your money, the part actually invested, might be earning several percent a year. Blend those two together into one portfolio return, and the idle part quietly pulls the whole number down. This is called cash drag, and most investors never work out how large it actually is.
Cash drag is the gap between the return your invested money could earn and the near-zero return your idle cash actually earns, averaged across your whole account. It is not a fee anyone charges you. Nobody takes money out of your account for it. It is an opportunity cost: money that could have been growing at a market rate instead sits still, and the account's overall return is the average of both parts, invested and idle, weighted by how much sits in each.
The bigger the idle balance and the longer it sits there, the more it drags down what you actually earn on the full amount of money in your account, even while the invested portion is doing fine on its own.
Not much. According to Bibit's own official FAQ, updated May 2026, RDN accounts held through BCA pay 0% to 1% per year, and RDN accounts through Bank Jago pay up to 2% per year. Rates vary by which bank administers the RDN and how large the balance is, but none of them come close to what invested capital can earn over time.
For comparison, Indonesia's benchmark stock index, IHSG, grew from 5,226.95 at the end of 2014 to 7,272.80 at the end of 2023, a compound annual growth rate of about 4.39% a year, according to Indopremier's IPOT News. That figure is the price index only, it does not include dividends, and any single year can land far above or far below that average, including 2026 itself, which saw IHSG fall roughly 38% before partly recovering. It is used here only as one real, cited long-run benchmark for what invested capital has actually done, not a prediction of what it will do next.
Take a portfolio worth Rp50,000,000. Assume the invested portion tracks that 4.39% long-run benchmark, and idle cash earns 1% a year, the higher end of what BCA's RDN pays. Here is what one year looks like at different levels of idle cash.
| Invested | Idle cash | Blended return | Value after 1 year | Lost to cash drag |
|---|---|---|---|---|
| 100% | 0% | 4.39% | Rp52,195,000 | Rp0 |
| 80% | 20% | 3.71% | Rp51,856,000 | Rp339,000 |
| 50% | 50% | 2.70% | Rp51,347,500 | Rp847,500 |
| 20% | 80% | 1.68% | Rp50,839,000 | Rp1,356,000 |
Blended return = (% invested × invested return) + (% idle cash × cash rate)
A quarter of your account sitting idle for a full year, the 80/20 row, already costs more than Rp300,000 on a Rp50,000,000 account. That is the direct effect. It gets bigger the longer it compounds.
Run the same 80% invested, 20% idle split for 10 years instead of one, with the gains reinvested each year. The fully invested account grows to about Rp76,834,980. The account with a fifth sitting idle the whole time grows to about Rp71,987,998. That is a gap of roughly Rp4,846,981, close to Rp5,000,000, lost purely to cash sitting idle instead of invested, on the exact same starting amount.
None of this means idle cash is always a mistake. Keeping some cash on hand for an opportunity, or while you research a decision, is normal. The point is knowing the actual size of the cost, instead of assuming a near-zero RDN rate is harmless because it is not a fee.
NetWort's Manual Assets feature has a dedicated "Cash" category where you can log your idle balance with its real annual rate, whatever your RDN or savings account actually pays. Add it there and your Dashboard will fold that cash into your blended portfolio return, so you can see the drag on your own numbers instead of a hypothetical Rp50,000,000 example. NetWort's Market page tracks current IHSG and IDX sentiment, useful context for judging what a realistic invested return looks like right now rather than relying on a multi-year average alone.
This is a different kind of return distortion than the one covered in why arithmetic and geometric mean returns diverge under volatility: that post is about how volatility makes an average annual return overstate your real result, while cash drag is about idle money quietly understating it. Worth knowing both, since either one can make a stated "return" different from what actually happened to your money.