There are multiple forms of calendar: Up-to-the-minute apps, in-built platforms and old-fashioned paper journals.
But they all have the potential to make your working day as productive as possible. How you use them, though, is personal.
Insider spoke to three productivity experts about how they get the most out of their calendars in a world where there is no "one size fits all" for maximum productivity.
These are their six top tips.
1. Make space for your toughest tasks
Fadeke Adegbuyi, senior marketing manager at productivity app company Doist, advocates making space for what computer scientist Cal Newport has defined as "deep work", or "activity performed in a state of distraction-free concentration that pushes your cognitive capabilities to their limit."
"When it comes down to actually getting things done, my solution is two-fold: getting rid of distractions and getting into a flow state," she said. "I'm a morning person and feel the most productive early in the day. I frequently dedicate my morning to writing and editing tasks."
Identifying the most important tasks requiring "deep work" and scheduling them into your calendar first is also the advice of Barnaby Lashbrooke, founder of virtual assistant platform Time Etc.
"I keep afternoons for major project work or for any tasks where I need the time to really think and plan," he said. "Work out when you do your best work and plan your sessions around those highs and lows."
2. Remember not all tasks are urgent enough to reach your calendar
Lashbrooke's full list of tasks on a given day may not even make it as far as his calendar.
He uses the Eisenhower Matrix, a method of prioritizing tasks based on how urgent they are.
"For entrepreneurs or business leaders, 'important' is defined as anything that helps you move your business closer to its short or long-term goals," he said. "Anything neither urgent nor important goes in the bin; it's not worth your time or effort."
Using this technique, Lashbrooke was able to cut his working hours from 100 to just 35 per week, allowing for more time with his three young children.
"I learned how to apply myself to the tasks that would help us reach our business goals and found that if I removed all distractions, and was militant about my use of time, I could get everything done in 35 highly productive hours a week, leaving the rest for my family," he said.
3. Make a master list of everything, then only add what you can do that day
Chloe Leibowitz is the cofounder of women-in-business consultancy We Are Tabono and a life coach who specializes in helping entrepreneurs set goals and define their vision. She maximizes her productivity by collating all of her tasks — regardless of whether they are big or small — onto a master list and adding only what she deems achievable that day onto her calendar.
"I like to work from a master list to avoid overwhelming myself," she said. "I can clearly see which tasks are actually projects that need to be further broken down, in order to pull out the exact tasks that need tackling."
Unlike most people, Leibowitz only uses a paper calendar. She relies on a written bullet journal to record her tasks and determine her priorities. "Apps get forgotten. There are still an awful lot of people who use — and benefit from — pen and paper."
4. Block off specific slots for specific tasks — and overestimate how long they'll take
Another technique used by Doist's Adegbuyi is time blocking, where people block off specific time slots for specific activities. "I know precisely what I'll be working on at 8am or 2pm," she said.
"The trick to making time blocking work is considering absolutely everything you need to complete — from writing an article, to eating lunch, to a one-on-one with a colleague — and adding a time estimate to each task."
Although it involves allocating one task to every time of the day, Adegbuyi suggested Time Blocking "requires some flexibility." She prefers to actively overestimate how long a task will take.
"If you suspect a task will take you an hour, block off one and a half hours instead. This will combat unrealistically overextending yourself."
5. ...But use "time boxing" to push yourself on tasks that are taking too long
To achieve her daily to-do list, Tabono's Leibowitz uses a technique called time boxing, a close cousin of time blocking.
Both techniques involve allocating fixed periods to specific activities, but where time blocking includes strictly reserving time within which you complete an activity, time boxing is meant to limit the time taken to complete a task, as you commit to moving on to another task when the time has elapsed.
"I work out how much time I need to spend on a task — be very specific here, don't be too generous. We can get most things done in a lot less time than we think if we remove distractions, like phones and notifications," she said.
6. Use your calendar as a prompt
Time Etc's Lashbrooke uses Google Calendar (using functions other online calendars have) as a live to-do list.
"Given that you can build in alerts and make Google Calendar publicly visible, it has greater potential to function as a productivity tool that keeps users focused and on track," he said.
"My calendar will give me a five-minute warning before I'm due to start a task, so I get a drink of water, get comfortable and make sure I'm not going to be distracted," he said. "A second alert tells me when to start the task, and another tells me when to stop and take a break."
"If your day is mapped out in black and white to the half-hour, it's far easier to be realistic about what you can achieve," he said.