You ran the Erlang C numbers. Your 9:00 AM interval needs 20 agents on the phones. So you schedule 20 people at 9:00 AM and expect to hit your service level.
Then one is in a coaching session, two are on break, one called in sick, and another is still logging into a system that froze. You have 15 people actually answering calls, and your service level falls apart.
That gap — between the people you pay and the people who are actually available — is called shrinkage. It's the most commonly under-planned number in workforce management.
What Is Shrinkage?
Shrinkage is the percentage of paid time that agents are not available to handle contacts. The standard formula is:
Shrinkage % = (Paid hours − Available hours) ÷ Paid hours × 100
If an agent is paid for 40 hours in a week but is only available to take contacts for 28 of them, shrinkage is 30%.
Planned vs. Unplanned Shrinkage
It helps to split shrinkage into two buckets, because you manage them very differently.
Planned shrinkage (you control the timing)
- Breaks and lunches
- Paid time off and approved vacation
- Training and onboarding
- Team meetings and huddles
- Coaching and 1:1s
- Offline work such as email, back-office tasks, or projects
Unplanned shrinkage (you can only forecast it)
- Sick days and call-outs
- Late arrivals and early departures
- Extended breaks or lunches
- System and technology outages
- Unscheduled bathroom, personal, or escalation time
Planned shrinkage can be moved around — you can schedule meetings away from your peak intervals. Unplanned shrinkage can't, so you need a percentage buffer to absorb it.
How to Calculate Shrinkage From Your Own Data
Don't guess. Pull a few months of data from your ACD and scheduling or timekeeping system, then:
- Total paid hours for the group over the period (everyone's scheduled hours, including time off).
- Total available hours — time agents spent logged in and ready, on a contact, or in after-call work.
- Subtract, divide, multiply by 100.
For example: a team is paid for 1,600 hours in a month, and 1,120 of those hours are productive and available. That's 480 hours of shrinkage, or 30%.
Track it by category too. If 12 points of your 30% come from time off, 8 from breaks, 5 from training, and 5 from absenteeism, you know where to look when you need to bring the number down.
Want to see this with real numbers? Open the calculator with a sample call center already loaded, then swap in your own.
Try it with sample data →How Shrinkage Changes Your Headcount
This is where shrinkage hits the schedule. Erlang C tells you how many agents need to be on the phones. To find out how many to schedule, you gross it up:
Agents to schedule = Agents required ÷ (1 − Shrinkage)
Take an interval that needs 20 agents on the phones:
- At 25% shrinkage: 20 ÷ 0.75 = 26.7 agents scheduled
- At 30% shrinkage: 20 ÷ 0.70 = 28.6 agents scheduled
- At 35% shrinkage: 20 ÷ 0.65 = 30.8 agents scheduled
Ten points of shrinkage is the difference between 27 people and 31 for the same interval. Across a full week, that's a very large payroll difference — and if you under-estimate it, a very large service level problem.
Common Shrinkage Mistakes
1. Double-counting breaks
If your shrinkage percentage already includes breaks and lunches and your schedule places breaks explicitly, you're counting them twice. Pick one: either keep breaks in your shrinkage %, or exclude them from the % and let the schedule model them interval by interval. The second approach is more accurate because it shows you where coverage actually dips when people step away.
2. Using one number for every day and every interval
Shrinkage isn't flat. Mondays have more call-outs than Wednesdays. Summer has more PTO than February. A single yearly average hides the periods where you'll get burned. Review it at least by season.
3. Not planning for it in the schedule shape
Grossing up headcount isn't enough if all your meetings land at 10:00 AM. Planned shrinkage should be pushed into your quietest intervals so that it doesn't compound with the peak.
4. Treating shrinkage as fixed
It's a management lever. Moving trainings to slow periods, tightening adherence, and fixing the one system that crashes every Tuesday can each recover several points. Every point of shrinkage you remove is headcount you no longer need to hire.
Rule of thumb: Many contact centers land somewhere between 25% and 35%. If yours is outside that range, it's worth checking that you're measuring it correctly before assuming you've found a problem or a miracle.
The Bottom Line
Erlang C gives you the number of agents you need working. Shrinkage turns that into the number of agents you need scheduled. Skip the second step and you'll hit your forecast and still miss your service level. If you're also working out the base requirement, start with our guide on how to calculate call center staffing.