The Rain Gauge

GIC publishes exactly one performance number: the rolling 20-year annualised real rate of return, in US dollars, above global inflation. No annual return. No dollar profit. No figure against a benchmark. The choice is defensible — the mandate is generational — and it is also the least falsifiable disclosure a fund can make, since each year one twenty-year window slides forward by one.

The gauge official

19 windows official

One series, two measures official

The chart above spans 19 annual reports, and a join runs through it. Reports up to FY2008/09 quote the 20-year return in Singapore dollars; from FY2009/10 GIC quotes it in US dollars. Currency of measurement changes a long-run return materially, so the early and late halves are not strictly the same number, and a straight line drawn across the join would be measuring two things. The basis is printed against every row for that reason.

What the wiggle actually encodes inferred

Two consecutive 20-year windows share nineteen years. Divide one compounded window by the other and everything shared cancels, leaving a single fact: how the year that entered the window compares with the year that left it, twenty-one years earlier. That ratio is the only single-year information this series ever discloses, and it can be computed exactly:

How to read a rolling number honestly

The fall from 4.6% in FY2022/23 to 3.4% in FY2025/26 is mostly the calendar, not the portfolio. Strong years at the start of the old window — the recovery after the dot-com bust — have rolled out, and the window now opens in the mid-2000s, just before the global financial crisis. The same arithmetic will push the number up again when 2008 and 2009 roll out in turn. A rolling average describes its whole window; the urge to read its year-to-year wiggle as current skill runs in both directions and should be resisted in both.

The next reading, bounded inferred

Next July's number is not a mystery — it is this year's window with one year swapped. The year that will leave is the year to March 2007; the year that will enter is the year to March 2027, most of which has not happened yet. Neither single-year return is published, so the table spans assumptions for both. Whatever markets do, the arithmetic confines the FY2026/27 print to roughly 2.1–4.1%: