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15 Percent Is Not A Magic Number For Primary Delegates

If you hear the phrase “delegate math” and remember 2016, you might have some nightmares. That’s because Republicans, who briefly kinda sorta looked like they might have a contested convention, have incredibly complicated delegate-allocation rules. Some states were winner-take-all in the GOP primaries. Some were proportional. Some states didn’t even really vote at all (!) or had voters chose delegates directly. It was a mess.

Democratic delegate rules are far more uniform from state to state — and they’re much simpler. But there are a couple of nuances that I can imagine people are going to get wrong.

One of them concerns the 15 percent threshold, which is a number that you’re going to be hearing a lot about. Democrats allocate their delegates proportionately among candidates who get 15 percent or more of the vote in a given state or district. So, for instance, if Bernie Sanders gets 42 percent of the vote in a certain state, Kamala Harris gets 18 percent, Joe Biden gets 14 percent, Pete Buttigieg gets 11 percent, Cory Booker gets 10 percent and Marianne Williamson gets 5 percent, then only Sanders and Harris would get state-level delegates, with Sanders getting 70 percent of the delegates1 and Harris getting the other 30 percent.

The part that’s easy to miss is in that term state-level delegates. In the Democratic primaries, only about 35 percent of delegates are actually allocated at the state level. The remaining 65 percent are allocated by district — usually by congressional district, although some states use different methods such as by county (Montana and Delaware) or state legislative districts (Texas and New Jersey).

This can make a big difference. In the example above, for instance, if Biden were to get 14 percent of the vote statewide, he probably would get some delegates because he’d likely be at or above 15 percent in at least some districts.

How many delegates is harder to say; it depends on how much variation there is from district to district. But for some rough guidance, I looked back at candidates who finished with between 10 and 20 percent of the vote in the Republican primaries in 20162 in states that allocated some of their delegates by congressional district.3 In the average district, there was about a 3-point gap between a candidate’s statewide vote share and that candidate’s districtwide vote share.

By performing a little math,4 we can extrapolate how many district delegates we’d expect a candidate to get given a certain statewide vote share. For instance, a candidate who gets 14 percent of the vote statewide, as Biden did in this example, would expect to achieve at least 15 percent in somewhere around 40 percent of districts, thereby receiving delegates there. Even a candidate who got 10 percent of the vote or less statewide might have a couple of strong districts where he or she received delegates, especially in a large, diverse state such as California.

On the flip side, a candidate who finished just above 15 percent statewide, such as Harris’s 18 percent in this example, would probably still miss out on a few district-level delegates by falling below 15 percent in some districts.

Overall, considering both state and district delegates, the relationship between statewide vote share and the share of statewide delegates looks something like this:

There’s still a big spike at 15 percent when the statewide delegates kick in, but it isn’t completely an all-or-nothing proposition; you’ll still get some delegates if you finish a bit below 15 percent, and you’ll still miss out on some if you finish just above 15 percent. The safest bet, of course, is to finish at 20 percent or higher, in which case you’ll not only get almost all of your delegates but will also have the chance to actually win the state.

Laura Bronner contributed research.


  1. Between them, Sanders and Harris — the candidates who finish at 15 percent or higher — get 60 percent of the vote in this example. Sanders’s 42 percent is 70 percent of 60 percent, hence he gets 70 percent of the delegates.

  2. I couldn’t really use data from the Democratic race because it was a two-way contest instead of the multi-way race Democrats have this year — and because both Hillary Clinton and Bernie Sanders were comfortably above 15 percent in almost every state.

  3. And where I could find records on how the vote was divided by congressional district, which wasn’t possible in all cases.

  4. Assuming that differences between state and district vote shares follow a normal distribution.

Nate Silver is the founder and editor in chief of FiveThirtyEight.