The Planning Department’s latest Housing Balance Report goes to the Planning Commission today and then to the Board of Supervisors next week to give them the hard numbers on how much affordable housing the citygains every quarter. The prognosis: Could be worse, but still not good.

Planning calculates the housing balance as the percentage of new affordable units over the number of new units overall for the past 10 years. This latest report includes (for the first time) public housing under projects like RAD (The Rental Assistance Demonstration) and HOPE SF (Housing Opportunity, Partnerships & Engagement), but only counts the net gain of new units, subtracting the number of units the city lost for one reason or another (more on that in a bit).

Here’s a formula to make it relatively easy:

[Net New Affordable Housing + Rehabs + HOPE SF & RAD + Entitled Units Yet Built], minus [Units Lost], divided by [Net New Housing Built + Entitled Units Yet Built] equals your Projected Housing Balance.

Right now the PHB is a little over 15 percent, which is not ideal. With all the building going on, there isn't enough BMR development to spike the numbers. Even worse, its balance would be 17.6 percent if we didn’t factor in the units that are entitled but yet to be constructed — meaning that upcoming projects are dragging the balance down. But the report also notes that three huge projects were excluded from the count on technicalities, which would have bumped the projection up to 21 percent.

Most revealing are the problem spots: In the last 10 years, District Six, which includes the Tenderloin and SoMa, has seen a net gain of 3,116 new affordable units, the highest volume of growth in the city. District Ten, which includes Bayview, is number two, with a comparably meager net gain of 758, followed by District Five (Fillmore/Western Addition), with 589.

The worst in the city? District Two, which includes Pacific Heights. It saw a net gain of only six affordable units in the last decade. District Four, which consists entirely of the Sunset, has some explaining to do as well: it has seen a net gain of only 10 units, one for every year.

In fact, the Sunset District’s housing balance is the absolute worst in the city, dropping a whopping 181 percent since January 2006.

How do we lose affordable housing? Owner move-in is the number one culprit, knocking out over 2,100 units (most commonly in District One, the Richmond District). The much-maligned Ellis Act is the number two method, removing 1,432 units (a plurality of them in District Three, which includes Twin Peaks).

Demolition is a distant third, blowing up 505 units since 2006, with the Sunset and southerly lying District 11 virtually tying for the most.

These regular housing report cards were mandated in 2014 by Prop K, which voters passed by a margin of nearly two-thirds. Prop K also mandated that the city build 30,000 new units by 2020, at least half of them dubbed affordable.