The Institute for Sustainable Development and Innovation (ISDI) offers the Field Guide to Timing the Olive Harvest free of charge. It is a standing guide for every season that helps growers base the harvest decision on the state of the fruit in their own grove, not on the calendar or on what the neighbours are doing. Harvesting too early means part of the oil has not yet formed, so the grower bears the cost of harvesting and transporting more fruit for less oil in the tin. Harvesting too late increases fruit drop, exposes the fruit to olive fly and disease, and lowers oil quality. The guide explains, step by step, the olive maturity index. The method was developed at the Venta del Llano experimental station in Jaén, Spain, and is used by the International Olive Council. Growers collect a sample of 100 olives, sort them into eight classes by skin and flesh colour, and calculate the index with simple arithmetic. A results table then tells them whether to wait, start harvesting, or harvest quickly. The test needs no equipment beyond a small knife, a cloth, a sheet of paper and a pen and takes about fifteen minutes per grove. The guide also includes reference photos of the eight classes, a worked example, and good practice for picking, transport and pressing to protect oil quality. Its last page is a printable field sheet for recording readings every 7 to 10 days. ISDI recommends confirming results with the local agricultural extension officer or the olive press. A joint publication of ISDI, supported by MOZARI3.com, the direct-to-consumer platform of Alwer Farms. Available in Arabic and English, and free to copy, print and share with credit to the Institute.