What Is an S-Curve in Project Management?

When you're a project manager, you'll take any edge you can get to ensure your project finishes on time and budget. Many variables affect the success of a project, and it's vital to predict the future so you'll be prepared to mitigate inevitable problems.

S-curves are a project manager's best friend -- not only in the planning phase, but over the course of a project. S-curves are one of those project management techniques that are basic to the job, but not everyone uses them correctly.

When you’re doing project planning, S-curves will help you visualize the path ahead and ensure you stay on it. This guide will help you understand S-curves, and how they’ll help your next project.

Overview: What is an S-curve in project management?

An S-curve refers to a mathematical graph that shows cumulative data over a period of time. That data may be anything from man-hours to costs. An S-curve helps you track a project's progress.

It's called an S-curve because the data forms an S-shaped curve on a graph, although the exact shape may differ depending on the project.

It forms an S because it starts slow, and then as the project ramps up the data speeds up causing the line to go rapidly upward. As the project begins to wind down, it hits a plateau and starts to flatten out to form the top part of the "S."

Benefits of understanding the S-curve

S-curves are useful because they help you visually track important aspects of a project and make predictions in cash flow or other key parameters. Here are a few of the specific benefits of understanding and using S-curves.

1. Helps track the project

The S-curve graph shows you real time what is happening in your project, allowing you to understand where the project stands and if you should make adjustments -- vital when it comes to cost management and project risk management.

2. Helps make predictions

The S-curve formula helps you map out the scope of work and make predictions critical to project success. For example, you could use an S-curve to plot your expected cash flow from start to finish -- identifying periods when you would need a loan to ensure liquidity during the project.

3. Helps prepare you

Many projects and startups must contend with managers who expect a linear growth line when they really should expect an S-curve.

As a result, they get frustrated by a lack of growth in the beginning, then get socked by a sudden increase in activity, and then have trouble ramping back down. Mapping out the project on an S-curve helps prepare them for the roller-coaster ride.

How the S-curve fits within the common project management phases

S-curve equations have a variety of uses within a project. These four ways will help ensure your next project is a success.

Map out expenditures vs. cash flow

You must know your cash flow compared to your project budget at all times. If you can’t predict what it will be, you could run into liquidity problems that could cause a project to grind to a halt.

An S-curve will predict expenditures and compare them to cash on hand at that time, which helps you avoid unpleasant surprises like running out of money and having to put things on hold.

The S-curve will show the company owner or a client what you expect to spend in the early part of the project and how that will increase exponentially once activity ramps up.

This helps stakeholders identify potential problems caused by cash flow issues. And if the actual expenditures start exceeding the prediction, or if cash flow is lower than expected, you can make adjustments before it’s too late.

Example: Susan, a project manager for a small software developer, is developing and marketing a new app. She plots an S-curve estimating expenditures over the course of the project and what cash the company will have on hand as the project progresses through various milestones. She delivers a report to management that assures them they will have the liquidity to handle this project. She gets the green light, with instructions to report back regularly on actuals vs. estimates.

Monitor project progress and evaluate performance

You can evaluate how your project is progressing by plotting it out on an S-curve schedule and comparing it to the prediction, which is also known as a schedule performance index (SPI).

This helps you anticipate a sudden change in the project. If, after a few weeks of relatively flat growth, there's been a sudden uptick in activity in the last few days, this is a sign that you are approaching the growth phase of the project, and therefore it's time to ramp up by bringing on more resources and labor.

By plotting your actual performance against the plan, you can see whether your performance is behind or ahead of schedule. It's a quick visual reference that prompts you to take action immediately. The S-curve also provides the information necessary to create a weighted scoring model to prioritize tasks.

Example: John, a construction manager, is erecting a new office building. He plots the progress of the project based on milestones completed on a graph and sees that the line shows he is behind his projections of where he'd be at this point. To keep the project on track, he cancels two optional but unnecessary tasks that consume man-hours and resources.

Predict needed man-hours

Hiring employees is not like ordering materials or equipment. You have to plan in advance for it, so map out expected man-hours for a project on an S-curve to ensure maximum hiring efficiency.

You won’t have too many employees standing around doing nothing during the early phases of a project, and you won’t scramble to hire staff as the project ramps up.

Using S-curves from prior similar projects -- or just making an educated guess -- map out a plan to have the right man-hours at the right time so you’re prepared no matter what phase of the project you're in.

Example: Craig, a vice president of operations for a tech company, is streamlining the IT department's support ticket process to speed up service. He maps out how many IT workers will be needed for each phase of the project, identifies each worker, and works with each of their managers to ensure they will be available during certain phases of the project, ensuring he is able to complete the project on time.

Track sales

S-curves are a good way to track product sales so you can predict future sales and make adjustments to production accordingly.

As marketing begins for a product, sales start slowly, but if the product makes an impact and people start purchasing it, eventually the line goes straight up necessitating a corresponding increase in production.

By monitoring sales volume, you will be able to communicate with production in a way that will avoid waste and increase efficiency.

Example: Tina, the sales manager for a small consumer drone manufacturer, has noticed orders are starting to level off after months of heavy sales. Using an S-curve analysis, she sees the company has reached market saturation and sales likely have plateaued. She informs production it’s time to ramp down drone manufacturing in order to avoid excess production and waste.

Try out project management software

Some software platforms allow you to create your own S-curves. Explore some of the project management software solutions The Ascent has reviewed to see if any of them make sense for your business.

Choose two or three, and start a trial to test out their features. In addition to S-curves, these platforms will help you handle all other aspects of project management, ensuring your next project is completed on time and on schedule.