Each new year, I try to implement a new productivity hack. Getting Things Done. Bullet Notebook. This year, I’m trying to manage my to do list with my calendar.

I realized a few years ago no arsenal of productivity hacks will prolong the working week, this February’s 29th day notwithstanding. That’s the challenge with to do lists - they lack commitment devices. A commitment device is a “way to change one’s own incentives to make an otherwise empty promise credible.” And what is a task on a list but an empty promise?

Have you used a to-do list app that’s asked you, Do you really have time to achieve all this today? Or decided on your behalf that the task you’re adding isn’t important? I haven’t. To do lists fail because the user’s good intention and optimistic aspirations go unchecked. For the software, the marginal cost to add a new task is zero. For me, it’s a quarter of an hour or more. Managing tasks by calendar is the only productivity hack that recognizes this reality.

Cue the calendar. When accepting a task, this philosophy proposes immediately allocating time in the calendar to accomplish it. Consider the due date, the time required, and the relative importance. Then book the slot.

This extra step reinforces the rigid time constraint immediately, not later when I’m staring at a lengthy to-do list and wondering where to begin. Each yes to a commitment is an implicit no to another. The calendar visualizes the tradeoff of each potential yes, making explicit the commitment to a task.

Last, I find scheduling tasks this way encourages batching work. An hour at the beginning and end of each day for email, but not in the rest of the day. Forty five minutes per week for quick calls. Bigger scheduling blocks seem to fall out of this type of task management and less context switching means more productivity.

Like all productivity hacks and New Year’s resolutions, managing tasks by calendar requires consistency and discipline. But this is one of the few productivity hacks that recognizes and reinforces the immutable constraints of time.