The 33% Rule

The 33% figure is not an arbitrary round number. It traces back to a hadith in which Sa'd ibn Abi Waqqas asked the Prophet Muhammad whether he could bequeath two-thirds of his estate to charity. The answer was no. Asked about one-half, the answer was again no. Asked about one-third, the Prophet permitted it, adding that even one-third was a lot. Islamic jurists, particularly in the Maliki and Hanbali schools, later generalized this principle across roughly seventeen unrelated areas of fiqh: one-third is treated as the boundary of what counts as a permissible, non-excessive portion, while anything above it is considered excessive. When 20th-century scholars built quantitative screens for modern stock markets, several adopted this same one-third boundary as the ceiling for a company's debt and interest-bearing investments relative to its size.

The Dow Jones Islamic Market Index caps debt at 33% of a trailing 36-month average market capitalization. FTSE Shariah caps both debt and cash-plus-interest-bearing items at 33.33% of total assets, with a monitoring band between 31.667% and 35% before a status change takes effect. MSCI Islamic uses the same 33.33% ceiling across three ratios (debt, cash and interest-bearing securities, and receivables plus cash, all against total assets), with a lower 30% entry buffer for new additions and a 35% exit buffer before removal. AAOIFI, by contrast, sets its debt and interest-bearing investment ratios at 30% rather than 33%, a stricter standard adopted because some scholars view the original hadith's context, a testamentary bequest, as different enough from tolerating interest-based activity that a tighter margin is warranted. PureInvest follows the AAOIFI standard, so a stock near the 30 to 33% range can show as compliant under one methodology and as a borderline fail under another.

The 33% figure shows up in a second, unrelated context that causes confusion: some retail halal screening apps classify a stock's non-permissible income ratio into three bands, compliant below 5%, "questionable" or "needs review" between 5% and 33%, and non-compliant above 33%. That is a different metric (income purity, not balance-sheet leverage) and a different convention, popularized by consumer screening apps rather than being a formal AAOIFI, DJIM, FTSE, or MSCI rule. All four major institutional standards actually cap non-permissible income at a flat 5% of revenue with no 33% tier in between; a company exceeding 5% fails the income screen under those standards regardless of how far past 5% it goes. Investors should be clear on which "33%" a given screener is referring to: the leverage ratio ceiling, or an informal revenue-band convention.