Each Monday, for every market on the T-bill monitor, take the rate at the most recent 364-day Treasury bill auction, counting a result for up to 120 days after its auction. The index is the simple average of those rates, published to three decimals. A week needs at least six markets to print. Rate measures are as each central bank publishes them (weighted average, stop rate, cut-off yield), compared without adjustment.
Equal weighting makes the index a measure of the typical African market rather than of its largest borrowers; weighting by debt outstanding would make it a reading of Egypt and Nigeria. The per-market table above lets anyone re-weight it. The 91-day version follows the same method on three-month bills. The index is revised when a central bank restates a result; revisions are rare and noted on the market’s page.
Quote it as: “The Afronomics African Sovereign Bill Index stood at 12.33% on 5 October 2026, down 7 basis points on the week and down 228 basis points on a year earlier.”