It is surprisingly difficult to predict the percentage of ballots that will come in early, via in-person voting or no-excuse absentee ballots, in the upcoming primaries. Many states have only recently begun to report individual voting histories that include the mode of ballot return, and even if they do have that information, even fewer provide the date.
At least one well-known data aggregator–Catalist--doesn’t capture the date of the ballot return on its permanent database, although that information is collected in real-time during election season.
Florida is a nice example: it does a wonderful job reporting early voting data, including the exact date that the ballot was cast. Individual no-excusse absentee records, however, are only available to registered party committees and candidate organizations.
To make things even more complicated, we know that Republican voters have historically tended to use no-excuse absentee ballots at a much higher rate than Democratic voters.
With all these caveats, the table reports the percentage of ballots that were cast prior to election day in the 2008 general election for selected upcoming states. Any state reporting less than 20% advance voting has been excluded. If you are trying to project backwards, most states now mail their domestic no-excuse ballots 45 days before the date of the election, the same time they are required to mail UOCAVA ballots/