How much time should you budget to write a book proposal? I’ve talked to writers from both ends of a spectrum: Some spend just a couple of weeks. They write a proposal of a few thousand words. Others spend a few months—or more. The most thorough write proposals of 25,000 words.

You certainly don’t need a 25,000-word proposal to sell a book. On the other hand, you probably won’t get a hearing from an editor based on just a couple of thousand words. So what’s a good guideline on timing?

I personally write proposals in the 8,000- to 12,000-word range. They take two to three months if they are my main focus, much more if I’m juggling other projects.

You might find it useful to see a tally of the work on the proposal for Merchants of Virtue: Herman Miller and the Making of a Sustainable Company, which I published in 2011 with Palgrave Macmillan.  The proposal ran 11,000 words, and this is what it took:

Total working hours, research and writing: 435

Total writing hours: 100 (estimated)

Total calendar time, start to finish: January 2009 to October 2009

Total documents reviewed: 75 (estimated)

Total books read: 5

Total interviews: 25

Total research travel: Two trips to Holland, Michigan ($1,654.00)

Total background research: Writing about the subject, off and on, for 15 years.

Total sales/negotiating time with publishers: 4 months (calendar time) 

During the proposal-writing period, I also wrote a story about Herman Miller for Strategy + Business magazine. That took 197 hours.

My proposal did not include a sample chapter, which many authors agents think critical, even if not mandatory.

You can see the proposal was a big investment, costing tens of thousands of dollars in sweat equity. What was the return on investment? Four publishers expressed serious interest. Two offered a contract.

I spent March 2010 to December 2010 writing the book, which ran 82,000 words. That took me another 1,500 hours or so—and three more trips for interviewing.

If you’re starting on a similarly sized book, my time budget offer guidance. But many factors come into play during a proposal, and you could cut the time in half—or double it. As a rule, proposals (and books) almost always take more time than you initially think.