How to make precise work time estimates

Marija Kojic

Last updated on: September 13, 2022

Precise time estimates help you plan and parse your work — as a result, you manage your time and errands properly.

But, it’s relatively easy to make a mistake in the estimated time to complete a project — mostly because people seem to be notoriously bad at guessing the time it takes them to finish something.

This miscalculation is quite common, and can happen either out of:

  • Optimism they’ll finish faster, or 
  • The urge to give themselves more time than they really need.

Therefore, the following 2 scenarios are most likely to happen:

  • You may estimate less time and rush the project in the end — instead of taking a few extra hours for revisions and necessary tweaks, or
  • You may estimate more time, finish earlier, and spend the remaining hours before the deadline procrastinating — instead of allocating this extra time to a different project.

This blog post will help you improve the precision of your work time estimations, as well as provide a free template for a useful time estimation calculator.

How to make precise work time estimates

The consequences of making poor time estimates (and how to avoid them)

Poor time estimates can and will disrupt your schedule and even push back your realistic deadlines. 

Consequently, late project delivery may turn the client you’re working with away from becoming a recurring one. 

Some clients may even mark the outcome of your project as a failure if you breach the estimated deadline.

All this shows just how much setting precise time estimates is crucial in cultivating a successful business

So, always bear in mind that all projects rely on time estimates and affect the schedules of everyone involved in them. 

So, how do you do time estimates?

Well, you make accurate time estimates for your project tasks, it is vital to break said tasks into smaller assignments. 

The activity of breaking tasks into smaller assignments is called pursuing “microproductivity.” 

Microproductivity consists of the following processes:

  • Identifying the main task,
  • Fragmenting said task into subtasks,
  • Listing all the subtasks,
  • Estimating the time required to complete each subtask, and even
  • Estimating the time you might allocate to breaks between subtasks.

By successfully adopting this skill, you’ll learn the right way to make all your tasks manageable and doable. 

For example, to “write a blog post” simply can’t be a single task, as it actually requires several different tasks — such as:

  • Conducting research,
  • Looking for relevant references,
  • Looking for relevant keywords to improve your content,
  • Writing an organized outline,
  • Writing the actual content,
  • Proofreading, spell and grammar check,
  • Writing effective headlines, 
  • Writing meta descriptions, 
  • Creating visuals, and
  • Uploading posts to WordPress.

In the example above, pursuing microproductivity means breaking one main task into 10 smaller assignments and further allocating a separate time slot to each. 

The psychological effect of this approach will:

  • Help us be more goal-oriented,
  • Boost our positive self-image,
  • Lead to less time spent procrastinating, and in the end
  • Help us make better time estimates. 

7 ultimate tips for making precise work estimates

To help you become an expert in time estimation, we’ve compiled the most important efficient estimation formulas, tips, and tricks.

Let’s dive right into the practical tips and explain the process of making precise work estimates in more detail.

Tip #1: Make a list of tasks you need to complete

You can’t go far without knowing what you need to do to get there.

So, before making time estimates, make sure you define a list of tasks you need to complete during a time period.

The best practice is to make a straightforward to-do list, one where you’ll lay out your errands and assignments for the day.

☐ Call Henry B.

☐ Meeting with the marketing team

☐ Write the project proposal

☐ Email Elinor about Becky’s party

☐ Attend a business brunch with clients

☐ Meeting with Luke S.

☐ Fill out the timesheet

Once you have your errands and assignments laid out this way, it’ll be easier to make estimates for the time it takes to complete them.

You’ll be able to allocate a certain amount of time to each assignment — and, as a result, you’ll be less likely to go outside of those time frames.

That’s why setting clear goals is by default of the utmost importance — and also why personal timekeeping will help you stay on top of things.

So, let us provide an example of such estimates and therefore, the total for the day. 

  • Call Henry B. — 10 minutes
  • Meeting with the marketing team — 25 minutes
  • Write the project proposal — 4.5 hours
  • Email Elinor about Becky’s party — 10 minutes
  • Attend a business brunch with clients — 1.5 hours
  • Meeting with Luke S. — 25 minutes
  • Fill out the timesheet — 5 minutes

In the end, you can easily calculate your total estimated time for the day by adding up these estimated hours (e.g. 7 hours and 15 minutes).

💡 Clockify pro tip:

Want to step up your game and work on mastering your time management skills in general? Check out this guide:

Tip #2: Put extra effort into time estimates for your priorities

Another important aspect of proper time estimation are your priorities.

By the rule of thumb, you should always allocate most of your time to priority errands and assignments. 

And, to get that right and minimize time wasters, you’ll have to put extra effort into defining the time estimates for both your priority tasks and your miscellaneous assignments.

So, your priorities are your most important and most urgent tasks — these are tasks that have a precise deadline you need to fulfill, or tasks that are crucial to the goal you want to accomplish for the day.

For example, you have to write a ~1,000 word Project Proposal for tomorrow — your ability to estimate the time for this task may influence whether you manage to complete it or not.

The first thing you need to do is make an outline for your proposal, and define the subheadings. They can serve as separate tasks, which you should then set separate time estimates for — in the following way:

  • Estimate the number of words you’ll write for each subheading:
    • (e.g. “Overview: 100–150 words”, “Goals: 200–300 words”, etc.)
  • Estimate the time needed to write and edit each subheading, in relation to the number of words:
    • (e.g. “100–150 words — 30 minutes”, “200–300 words — 1 hour”, etc.)
task name assignee estimation

Once you’re done estimating the time for the subheadings, add these numbers up — this is your total estimated time for the priority task.

task based

For the best results for you specifically, you ought to calculate your biological prime time — i.e. the time during the day when you are most likely to be productive, focused, and motivated to complete your tasks. This is the time you’ll be most likely to finish your tasks faster — so save these time slots for your priority tasks.

On an additional note, if you allocate the longest amount of time to your priority task — you’re essentially signaling yourself that you should focus all your energy on this task.

write project proposal to-do list

Tip #3: Use the Time Estimation Formula

When looking for a formulaic approach to defining the number of days it’ll take you to finish a project, you don’t need to look further than the Time Estimation Formula, based on The Program Evaluation and Review Technique (also known as PERT).

So, what are the types of time estimation in PERT?

pert chart example

PERT is a method of calculating project time — it involves a time estimation formula that takes into account your:

  • Optimistic time estimate (A)
  • Most likely time estimate (B)
  • Pessimistic time estimate (C)

Let’s look at an example, to better understand how PERT works.

The optimistic time estimate (A)

This is the shortest possible amount of time you think will take you to finish a type of project — it’s also known as the best-case estimate, and it implies smooth sailing throughout the project.

In short, the optimistic time estimate applies when everything is going perfect:

  • Everyone in your team finishes their work on time,
  • No revisions are necessary,
  • No problems with the budget, and
  • No problems with the materials and equipment.

For example, past experiences have taught you that the optimistic time estimate for a type of project in your team is 225 days, meaning that A = 225.

The most likely time estimate (B)

This is the realistic amount of time you think will take you to finish a type of project. 

It’s also known as the most likely estimate, and it implies an average voyage throughout the project.

The most likely time estimate applies when everything about the way your project is progressing is average:

  • Everything goes generally according to plan,
  • Most people finish their tasks on time, and
  • There’s an average number of revisions needed.

For example, past experiences have taught you that the most likely time estimate for a type of project in your team is 360 days, meaning that B = 360.

The pessimistic time estimate (C)

This is the longest possible amount of time you think will take you to finish a type of project. 

It’s also known as the worst-case estimate, and it implies icebergs everywhere throughout the project.

The pessimistic time estimate applies when you encounter several problems before finally completing the project:

  • Most of your team members have issues finishing before the deadline,
  • A lot of revisions are needed before submitting the project for final review,
  • Major problems with your materials and equipment, and
  • Major problems with your budget.

For example, past experiences have taught you that the pessimistic time estimate for a type of project in your team is 375 days, meaning that C = 375.

💡 Clockify pro tip:

Delays in project execution happen to everyone, don’t beat yourself too much about it. Check out our list of the best project management techniques, practices, and tools instead.

The actual calculation — The Time Estimation Formula

The Time Estimation Formula takes into account that all these types of estimates are equally possible, and the formula itself (E) goes as follows:

E = (A+4B+C)/6

If we take the listed optimistic (A = 225), most likely (B = 360), and the pessimistic time estimate (C = 375), here’s how the numbers stack up:

E = (225+4*360+375)/6

E = 340

So, you’re most likely to finish the said project within 340 days. 

But, as complications happen, you’ll need to expand your calculation and your time frame — this is where standard deviation kicks in. 

The formula goes as follows:

SD = (C-A)/6

The standard deviation formula takes into account only the optimistic and pessimistic time estimates and tells you how accurate your total time estimate really is:

SD = (375-225)/6

SD = (150)/6

SD = 25

If the standard deviation is 25 days, that means that the project can take anywhere between 25 days more than what the time estimation formula tells you, and 25 days less. So, in the end, this type of project can take anywhere between 315 and 365 days.

Tip #4: Use a project duration calculator

A project duration calculator is based on the previously talked about:

  • Time Estimation, and 
  • Standard Deviation formulas.

You’ll still get the roughly estimated number of days you need to finish the project — but, you’ll get it faster, because the calculation will be handled automatically.

project duration calculator

Here’s how you can create a simple project duration calculator in Excel, by using:

  • The Time Estimation Formula (E = (A+4B+C)/6), and
  •  The Standard Deviation Formula (SD = (C-A)/6).

For the “Time estimation formula” cell, write: =ROUNDUP((C4+C5*4+C6)/6)

For the “Standard Deviation” cell, write: =ROUNDUP((C6-C4)/6)

For the “Shortest estimated project duration” cell, write: =ROUNDUP(C8-C9)

For the “Longest estimated project duration” cell, write: =ROUNDUP(C8+C9)

Now, you need to enter your data into the following cells:

  • Optimistic time estimate,
  • Most likely time estimate, and 
  • Pessimistic time estimate.

Once you’ve done so, the data will point out your estimated time and standard deviation.

Additionally, the shortest and longest estimated duration will be calculated automatically.

🔽 Download your Project Duration Calculator for free

Using the ROUNDUP function is optional — but highly recommended because you’ll round up the estimated number of days to a whole number.

To use the same formulas for additional projects, simply hold and drag your cursor at the edge of the cells containing the formulas, as shown below.

So, if you enter “145”, “234”, “345”, you’ll get that your estimated time to finish the project is 238 days, with a standard deviation of 34 days — meaning you’ll likely take between 204 and 272 days to finish this type of project.

💡Clockify pro tip:

Looking for an easy way to calculate your work hours in Excel? Then check out our guide on how to create functional timesheets in Excel:

Tip #5: Track your time

A project duration calculator tells you how many days you’ll likely need to finish a project, which is useful for giving a rough estimate to the client.

But, you’ll also need a more precise estimate, to plan and parse your work in detail, as well as create a functional schedule to follow while working on a said project — this is where a time tracker becomes crucial.

A time tracker makes estimating time an exact science. It tells you how much time you’ve spent on previous projects in total — in hours, minutes, and seconds — and, it lets you identify the tasks that took most of your time. 

It also tells you what type of work you’ve spent most of your time on — for example, “front-end” or “back-end” tasks.

front end

Why does time tracking matter for project management?

Well, for starters, by keeping time tracking records, you’ll be able to make time estimates for a specific type of project, that are actually based on your completely verifiable past experiences.

To gather your time tracking data, you can easily start a timer each time you start working on a task, and associate it with the right project.

Once you’re done working on this task, stop the timer. By doing so, you’ll be adding this time to your total time for that project.

There’s also an alternative to this process — you can manually enter the time in your timesheet, after the completion of a specific task.

Adding time to total project time

By the end of the project, you’ll have the exact time you’ve spent on it now, and are likely to spend on the same type of project in the future — so, you’ll be able to give a precise estimate to your clients.

In addition, you’ll be able to distinguish between your billable and non-billable hours, as well as understand how much money you’ve earned working on the project — thereby helping you improve your project cost management in the future.

How you can track time to define time estimates: example #1

You can even turn hours into days and see how accurate your project duration calculator really is.

Let’s take an example — you’ve spent 283 hours and 39 minutes on a project. 

Well, that easily translates to 35.5 days you have spent working on this project for 8 hours a day.

total and billable

But, this isn’t the only way to manage and define time estimates within a time tracker.

How you can track time to define time estimates: example #2 

Clockify also offers an estimation system where you’ll be able to define estimates for tasks and the project overall, before comparing your real time tracking results with these estimates.

edit project

So, once you start tracking time, you’ll be able to compare your real-time progress with your estimates as you work.

You’ll also be able to see the percentage of completed work, compared to your estimates at all times.

website development task

This way, you’ll not only be able to see that your original time estimates were off, but you’ll also be able to see by how much. 

Therefore, you’ll be working on your skill of estimating and setting the right project timeline, while at the same time you’ll be avoiding the pressure caused by unrealistic deadlines.

Tip #6: Calculate the time you’ll waste

When making time estimates for a project, it’s easy to overlook the time you’re bound to waste — so, don’t forget to account for the following: 

  • Interruptions, 
  • Distractions, and 
  • Idle procrastination.

First, list the activities you likely “waste time” on every day at work.

Then, assign them a time estimate:

  • Going out for a smoke every 2 hours — 25 minutes
  • Going out to the nearby bakery to buy scones for an afternoon snack — 15 minutes
  • Going to fix a cup of coffee every 3 hours — 15 minutes
  • Chatting with colleagues — 45 minutes

You can even add the time you spend on meetings and sorting out your email inbox to this wasted time — after all, these activities don’t contribute to finishing the project and only take you away from real priorities:

  • Meetings — 1 hour and 20 minutes
  • Inbox management — 1 hour

You can make time estimations at the top of your head for these activities, or you can make a weekly experiment and track the exact time it takes you to finish these activities per day.

Tracking wasted time to make precise time estimates

For example, if you track the following results for daily meetings:

  • 40 minutes on Monday
  • 45 minutes on Tuesday
  • 30 minutes on Wednesday
  • 45 minutes on Thursday
  • 40 minutes on Friday

Then, you can take 40 minutes as your average time for a meeting in future estimates:


Tracking wasted time to estimate how much you spend focused on the project

In the end, to get the total wasted time per day, just add up the numbers — let’s say that all the listed time wasters, from coffee breaks to meetings, add up to 4 hours.

So, if you work 8 hours per day, and waste 4 hours, you essentially spend only about 4 hours focused on the project. 

Properly calculating the total amount of your wasted time in a day will improve your precision in making work estimates. This step will help you make managing time easy.

After all, if you’re aware that you actually have only half the time you thought you had to complete your tasks, you’re more likely to set different and more realistic deadlines. Or even better, you’ll try to reduce your time-wasters and thereby improve your productivity levels.  

💡 Clockify pro tip:

If you’re wondering how to adequately identify inefficiency, check out this thorough guide. Tips and tricks included.

Tip #7: Schedule additional time, just in case

The data you get from your time tracker shows the exact time you’ve spent on similar projects before, and how much you’re likely to spend on it next time.

So, in 9 out of 10 cases, if you’ve spent 71 days on a project (or 283 hours and 39 minutes hours for 4 hours/day), you’ll likely spend a near similar amount of time on it next time.

But, just in case, allocate some additional time to this project, for unexpected problems and shortcomings that usually come with the 10% of such projects. 

You’re probably aware of the saying: “Better safe, than sorry.”

You never know when this percentage might increase, and when you’ll need additional days and hours to round up the project to the complete satisfaction of your client.

Conclusion: Precise work estimates matter (and you will get better results over time)

In the end, making precise time estimates isn’t that difficult. 

You’ll just need to:

  • Parse your work into daily tasks and make estimates for these separate tasks,
  • Put extra energy into correctly estimating time for priority tasks,
  • Make the effort to track the time you spend on projects and tasks,
  • Account for the time you waste every day, and
  • Account for the additional time you may need to finish the project.

For extra flair, you can use PERT’s Time Estimation Formula and rely on a simple Project Duration Calculator, to calculate your daily estimates. 

As a result of following these tips, you’ll make your time estimates precise and accurate, as well as planning your schedules easier. Project management is all about dependencies, and these tips will help you have a deeper understanding of your workflow, which will be reflected in your upcoming projects. All this will ensure your clients view you as a reliable professional, who keeps to their word.

✉️ Have you ever tried a technique for making your time estimates more precise? Do you have any recommendations for useful calculators that we haven’t mentioned yet? Feel free to share your 2 cents. Write to us at and we will consider featuring your opinion in this or one of our future pieces. And, if you liked this article, share it with someone else you know will find it useful.

Author: MarijaKojic

Marija Kojic is a productivity writer who's always researching about various productivity techniques and time management tips in order to find the best ones to write about. She can often be found testing and writing about apps meant to enhance the workflow of freelancers, remote workers, and regular employees. Appeared in G2 Crowd Learning Hub, The Good Men Project, and Pick the Brain, among other places.

Free time tracker

Time tracking software used by millions. Clockify is a time tracker and timesheet app that lets you track work hours across projects.


Learn more Arrow Right Primary
Clockify time tracker
Watch demo (12:35)
Closing video