Do you really think Richard Branson and Bill Gates wrote long to-do lists and prioritized items as A1, A2, B1, B2, C1 and on and on?

In my research into time management and best practices for productivity, I've interviewed over 200 billionaires, Olympians, straight-A students and entrepreneurs. I always ask them to give me their best time management and productivity advice. And none of them have ever mentioned a to-do list.

There are three big problems with to-do lists.

First, a to-do list doesn't account for time. When we have a long list of tasks, we tend to tackle those that can be completed quickly, leaving the longer items left undone. Research from the company iDoneThis indicates that 41% of all to-do list items are never completed!

Second, a to-do list doesn't distinguish between urgent and important. Once again, our impulse is to fight the urgent and ignore the important. (Are you overdue for your next colonoscopy or mammogram?)

Third, to-do lists contribute to stress. In what's known in psychology as the Zeigarnik effect, unfinished tasks contribute to intrusive, uncontrolled thoughts. It's no wonder we feel so overwhelmed in the day, but fight insomnia at night.

In all my research, there is one consistent theme that keeps coming up.

Ultra-productive people don't work from a to-do list, but they do live and work from their calendar.

Shannon Miller won seven Olympic medals as a member of the 1992 and 1996 U.S. Olympic gymnastics team, and today she is a busy entrepreneur and author of the new book, It's Not About Perfect. In a recent interview she told me:

During training, I balanced family time, chores, schoolwork, Olympic training, appearances, and other obligations by outlining a very specific schedule. I was forced to prioritize...To this day, I keep a schedule that is almost minute by minute.

Dave Kerpen is the cofounder of two successful startups and a New York Times bestselling author. When I asked him to reveal his secrets for getting things done he replied:

If it's not in my calendar, it won't get done. But if it is in my calendar, it will get done. I schedule out every 15 minutes of every day to conduct meetings, review materials, write, and do any activities I need to get done. And while I take meetings with just about anyone who wants to meet with me, I reserve just one hour a week for these "office hours."

Chris Ducker successfully juggles multiple roles as an entrepreneur, bestselling author and host of The New Business Podcast. What did he tell me his secret was?

I simply put everything on my schedule. That's it. Everything I do on a day-to-day basis gets put on my schedule. 30-minutes of social media-on the schedule. 45-minutes of email management-on the schedule. Catching up with my virtual team-on the schedule...Bottom line, if it doesn't get scheduled it doesn't get done.

There are several key concepts to managing your life using your calendar instead of a to-do list.

First, make the default event duration in your calendar only 15-minutes. If you use Google Calendar or the calendar in Outlook it's likely that when you add an event to your calendar it automatically schedules it for 30, or even 60, minutes in length. Ultra-productive people only spend as much time as is necessary for each task. Yahoo CEO, Marissa Mayer, is notorious for conducting meetings with colleagues in as little as 5 minutes. When your default setting is 15-minutes, you'll automatically discover that you can fit more tasks into each day.

Second, time-block the most important things in your life, first. Don't let your calendar fill up randomly by accepting every request that comes your way. You should first get clear on your life and career priorities and pre-schedule sacred time blocks for these items. That might include two hours each morning to work on the strategic plan your boss asked you for. But your calendar should also include time blocks for things like exercise, date night or other items that align with your core life values.

Third, schedule everything. Instead of checking email every few minutes, schedule three times a day to process it. Instead of writing "Call back my sister" on your to-do list, go ahead and put it on your calendar or even better establish a recurring time block each afternoon to "return phone calls."

That which is scheduled actually gets done.

How much less stress would you feel, and more productive would you be, if you could rip up your to-do list and work from your calendar instead?

Kevin Kruse is a New York Times bestselling author and founder of The Kruse Group. He is the author of 15 Secrets Successful People Know About Time Management. Take his free time management style assessment and improve your productivity.