Have you ever wished you had a couple of extra days to finish off a project task? When real life gets in the way, it can be useful to have a little bit of contingency in the system to cope. That’s buffer time. Buffer time is additional time assigned to tasks (or at project level) in the project schedule to account for risk, uncertainties and unforeseen delays. \
You’ll also hear it called contingency and some teams may use ‘slack’ as an interchangeable term for extra wiggle room on the project schedule.
Whatever your team calls it, buffer time is crucial for increasing confidence in being able to achieve project milestones.
Buffer benefits
Contingency time on project tasks is useful because:
- It helps manage uncertainty and risk. Projects often face unforeseen challenges such as delays in task completion, scope creep, or resource shortages.
- It helps mitigate inaccurate estimates. Your subject matter experts might be the best in the world, with estimating techniques like scenario planning and Monte Carlo simulations to support their work, but they could still make mistakes. Forecasting task durations is difficult. Buffer time helps accommodate inaccuracies.
- It helps mitigate external factors. There have been plenty of ‘black swan’ events that businesses haven’t predicted for, such as severe weather, global conflict and the pandemic of 2020 and beyond. These can all cause supply chain disruption and impact the team. Even something simple like a delay on the client’s side could cause scheduling problems unless you’ve got a buffer to protect against the impact.
Including buffer time in the schedule
So, let’s say you want to add some contingency to a project task. How much do you add? Ideally, you’d want to work out the risk level of each task and add an appropriate amount based on that. A task which has been completed many times before and is completely within the team’s control wouldn’t need much (if any) extra time. You have a high degree of confidence that the estimate is correct.
A task that the team hasn’t done before, that relies on external parties and that carries a lot more overall risk is a different story. There is no right or wrong answer to how much buffer to add, but we’d suggest between 10% and 20% – use your professional judgement. A low-risk project will need fewer blocks of contingency than a high-uncertainty project.
Tell stakeholders about contingency time
Transparent communication about buffer time helps set realistic expectations. When stakeholders understand that buffers are intentional and calculated, they are more likely to be supportive when delays occur. They’ll know you have planned for the delay and have a strategy to avoid it from impacting the overall end date.
Explain to stakeholders that contingency time is a proactive strategy, not a sign of inefficiency. You aren’t adding a buffer because you don’t trust the team! It’s a proactive way of managing external influences and risk.
Watch out for padding
Buffer time sounds a lot like padding estimates, but it is different. Legitimate contingency time is based on an assessment of risk, understanding the external factors and being transparent with the team about the unknowns. Padding is where estimators add in a bit extra without transparency, and that’s to be avoided!
Where to put buffers
Not every task will need a buffer allocation. Extra time should be added where it is going to do the most good at keeping you on track. For example, focus on critical path tasks, key milestones, and risk-heavy areas.
If you are working in a predictive environment with a linear plan, add contingency blocks at task level, phase or stage level or at the project level overall. We find it most useful to break up the contingency and associate it to a particular workstream or stage of the project so it can be seen, managed and used at that time.
Agile teams would consider leaving time between sprints or allowing for extra capacity within a sprint to account for any unforeseen issues. With both methods, it’s easier to accommodate contingency as you go along instead of bolting it on to the end of the project. Leaving all the contingency to the end makes it harder to manage, so let’s talk a bit about that now.
Managing contingency time
While your buffers are there to be used, it’s important that they are used sensibly and that the time is tracked accurately. You don’t want to get to the middle of the project and find that all the time has been used up already. Keep track of how the buffer time is being used and allow that to inform scheduling decisions going forward.
For example, if you notice that one team is drawing heavily on contingency, it would be worth reviewing all their schedule estimates to see whether they are inaccurate generally across the project. Then you could add extra time as necessary to their work, if that fits with the schedule.
Project scope and the risk level of the project is likely to change as the work progresses, so keep your contingency time under review. It’s important to strike a balance between ensuring buffers are based on realistic risk assessments and managed carefully.
When used strategically, buffer time serves as a safety net, enabling the team to navigate unforeseen challenges without burning out or letting down a client. Contingency planning can be a proactive tool to safeguard your projects, ensuring smoother delivery and stronger outcomes even when the unexpected happens. Then, when real life does get in the way of hitting a deadline, you will still be able to manage the delivery to time because you’ll have adequate buffer time in the schedule.