Open up your current to-do list and take a look at it. How many of your tasks have a time estimate next to them? If you are like the majority of people, probably none. When writing out to-do lists, most of us only ask ourselves one question — what do I need to do? — and not how long will I need to do it

This approach usually results in an intimidating list that goes on for three, four, even five pages: “Register car, do taxes, update resume, paint the bathroom, call Aunt Ethel, buy groceries, do the laundry, etc. etc.” In looking at the list, you may ponder how you feel about each task — “I like this one, I think I’ll do that today,” “I dread that one — maybe tomorrow…” — but you probably don’t consider how long it will take.You are approaching your tasks qualitatively, not quantitatively.

Yet, the difference between good and bad time managers pivots on the asking of this critical question: How long will it take? Good time managers calculate how long things take and build the time they need into their schedules. “I’ll need a full two hours to write this report, better do it first thing Monday morning, before my 11:30am meeting with the board.” Or perhaps your afternoon meeting is cancelled and you suddenly have 30 minutes to spare. Having already calculated that it’ll take you approximately half an hour to read and respond to your client’s recent proposal, you can turn your attention to the task at hand rather than mindless responding to emails or, worse yet, wasting the time trying to decide which of your many to-dos you could be working on.

Rest assured, people who are good at estimating how long things take aren’t born with magical powers, though they may be more mathematically inclined. In fact, once you understand the concept, it’s a simple skill that anyone with a calculator and timer can master. For example:

My brother, Steve, is one of the best time managers I know. He got through his demanding medical school studies by using extremely impressive calculating skills. At the beginning of each semester, he’d figure out how many pages he had to read for each course. Then he’d calculate: “It takes me an hour to read, high-light, and study ten pages. I’ve got six five-hundred-page textbooks to read this semester. That’s a total of three thousand pages to read. At ten pages per hour, I’ll need three hundred hours to get through it all. With twelve weeks in the semester, that means I need to read five hours a night if I want to take weekends off.”

Perhaps this seems like it’s going overboard. But imagine how relaxed Steve felt knowing that as long as he studied fifty pages a night, he’d make his goal. If he missed a night, he had enough wiggle room to make up for it on another night or over the weekend. By breaking the project down into a series of manageable steps, the task no longer loomed so massively over his head. No pressure, less stress, no surprises.

Estimating how long things take is a skill anyone can master. It may take you two weeks of practice to get the hang of it, but you can, without a doubt, learn this critical skill. With it, you unlock the ability to maximize your productivity and efficiency, using time to your advantage to get more done each day. It all starts with asking yourself a simple question: how long is this going to take?