What if all patients could be seen on the day they call?

Why do we have to wait days, weeks, or even months for a doctor's appointment? Such delays have become so routine that they seem normal. But if some of the most popular restaurants can take same-day reservations, why should run-of-the-mill doctors routinely make patients wait and wait and wait?

In fact, they shouldn't. The challenge of reducing waiting times is a classic queuing problem in operations research. Professionals in all sorts of service industries, from restaurants and hotels to banks and department stores, have faced it in one form or another. Most of them handle the juggling of clients  far better than physicians, despite the lower stakes. Mounting evidence shows that doctors can see patients quickly, too—even in perennially backlogged practices—and that when they do, they benefit themselves and the people they treat.

The road to reform is called "open access" (or "advanced access" or "same-day scheduling"). Dozens of papers have been published showing how practices around the country have done it, starting in 2000, when Dr. Mark Murray and colleague Catherine Tantau wrote about their experience of reducing the wait at a Kaiser Permanente clinic near Sacramento from 55 days to just one. Since then, clinics in Texas, Illinois, Minnesota, and elsewhere have similarly cut down patients' waiting times. The Palo Alto Medical Foundation offers same-day appointments, as does the Veterans Administration, the Mayo Clinic, and even some solo physicians.

When a patient calls in the morning asking to see a doctor who uses open access, the office offers an appointment for that same day. Why are there openings available? Well, the main reason most doctors defer today's work to some time in the future is that today's schedule is clogged with appointments made weeks ago. Doctors following the same-day scheduling model, on the other hand, are free today because they saw yesterday's patients yesterday. Using open access, doctors might still schedule some early-morning appointments in advance, for follow-up visits or for patients who actually prefer a future appointment. But the key is that they keep most of their time free for same-day visits and fill up their schedules as the day goes.

This sounds simple, and it flows easily once the system is up and running. But getting open access off the ground takes hard work. Doctors have to chip away at their backlogs, a task that typically takes several months of overtime. That's because during the transition, practices must meet their earlier obligations while at the same time offering same-day visits, to keep future dates clear. They also have to cope with fluctuating demand: If Monday is always the busiest day of the week, the office has to work longer hours on Mondays for open access to run smoothly.

Doctors also have to make sure their practices don't take on more patients than they can handle. The total number of patients in a practice, called the panel size, is crucial because it determines the demand for service on a typical day. Obviously, the larger the panel, the higher the number of expected daily appointments, and if demand outstrips supply, waits are inevitable. Yet many doctors have no idea whether their panel size is too large. They track only the patients they see, not the patients who wanted an appointment but didn't get one. That's a formula for underestimating actual demand for service.