The custom of reading a passage from the Prophets, the haftorah, is ancient and obscure. The Talmud deals with it¹ but does not elaborate on the source or the reason for the custom. According to one early source², it is no less old than the custom of public Torah reading itself, traditionally held to have been instituted by Ezra.

This post will not shed any light on these questions, but instead answer a far simpler one: how are the haftarot of the annual cycle distributed between the different books of the Prophets? As "all are subject to luck, even the Torah scroll in the ark"³, which books are fortunate enough to be read more often than others?

To this end I put together a table of the annual readings and did a quick data analysis⁴. For each book I calculated the number of haftarot it has, number of chapters, and the ratio of the two (to give a sense of haftorah frequency relative to size). My takeaways were:

• The biggest single source of haftarot is Yeshayahu. (With the שבע דנחמתא freshly behind us, this may not feel surprising!)
• When measuring relative to size, Trei Asar as a whole is the largest (scoring 0.36), with multiple haftarot coming from Hoshea, Amos and Zecharia, while the books of Ovadia and Yona are read in their entirety. (Yoel contributes just a snippet at the end of the haftorah of Shabbos Shuva, while Nachum, Chavakuk, Tzafania and Chagai are entirely absent.)
• However, if considered separately, both Malachi (0.67) and Melachim Alef (0.45) have higher scores.
• If we take “Deutero-Isaiah” (ישיעהו השני⁵) as an independent book, it is the largest single source of haftarot (15, scoring 0.58). In fact, the rest of Yeshayahu has a mere 3 haftarot, giving it the lowest score (0.08) of any book. (But one of these is the famous reading of Shabbos Chazon, which surely counts for something…)
• There are roughly twice as many haftarot from the (mostly non-narrative⁶) Latter Prophets compared to the Early Prophets (50 vs 26). This is partly due to their greater length, and partly, I suspect, because it is harder to find thematic overlap between narrative prophecies and the weekly Torah portions.

I took the list of haftarot from here. In cases where customs differ, I followed the Ashkenazi rite (there are only a few cases where different communities read from entirely different books). I included Rosh Chodesh and holiday readings, but not that of יום עצמאות. If a haftorah included parts from different books, I included only the main part of the reading.