Staffing a 24/7 operation is not as simple as multiplying by three shifts. A single position that must be covered every hour of every day requires 8,760 hours of coverage per year, but no single employee provides more than about 1,800–1,900 net available hours after accounting for vacation, sick time, holidays, training, FMLA, and unscheduled absences. The ratio of required hours to net available hours is the relief factor—and getting it wrong means either chronic overtime (too few people) or excess labor cost (too many).
This guide walks through the math of relief factor calculation, typical absence budgets by industry, how different rotation patterns affect headcount requirements, and the trade-off between planned overtime and additional hires for round-the-clock coverage.
What Is a Relief Factor?
The relief factor (also called the coverage factor or staffing ratio) is the number of employees needed to keep one position filled at all times. It is calculated as: Relief Factor = Annual Coverage Hours ÷ Net Available Hours Per Employee. For a position that must be covered 24/7/365, the annual coverage requirement is 8,760 hours. If each employee provides 1,850 net available hours, the relief factor is 8,760 ÷ 1,850 = 4.73—meaning you need 4.73 FTEs to guarantee one person is always on station.
In practice, you cannot hire 0.73 of a person, so you round up to 5 and either accept some bench time or reduce overtime in other areas. Alternatively, you staff at 4 and plan for the gap (about 360 hours/year, or roughly 7 hours/week) to be covered by overtime, temporary staff, or cross-trained personnel from other roles. The decision depends on whether overtime or idle time is more expensive for that position.
Relief factors for common scenarios: a standard 5-day, 8-hour operation with typical absences needs a relief factor of about 1.15–1.25 (one relief person per 4–7 positions). A 24/7 operation on 8-hour shifts needs 4.5–5.5. A 24/7 operation on 12-hour shifts needs 4.0–4.8. The range depends entirely on your absence profile—and most managers underestimate absences by 15–25%.
Headcount Coverage Calculator
Calculate minimum staffing for 24/7 operations using relief factor analysis. Accounts for PTO, sick leave, training, FMLA, and workers comp with rotation presets including DuPont and Pitman.
Building Absence Budgets
The accuracy of your relief factor depends entirely on a realistic absence budget. Start with the contractual and statutory absences: vacation (typically 80–160 hours/year depending on tenure), holidays (56–96 hours for 7–12 paid holidays on an 8-hour schedule), and scheduled training (16–40 hours/year). These are predictable and should be the starting point.
Then add the less predictable categories: sick leave utilization (not the accrual, the actual usage—typically 24–48 hours/year), FMLA leave (the average across the workforce, not the maximum allowed), workers' comp lost-time cases (prorated), bereavement, jury duty, military reserve duty, and unexcused absences. BLS data shows that the average private-sector absence rate is about 2.8% of scheduled hours (roughly 58 hours/year for a full-time employee), but manufacturing and healthcare run higher at 3.2–4.0%.
The mistake most managers make is using the accrual or policy maximum instead of actual utilization. Your company may offer 10 sick days (80 hours) per year, but if average utilization is 4 days (32 hours), use 32—not 80. Conversely, many operations undercount unscheduled absences because they are tracked informally or attributed to other categories. Pull 12 months of actual timekeeping data, categorize every non-productive hour, and build your absence budget from reality, not policy.
Industry Benchmarks
Relief factors vary significantly by industry due to different absence profiles, regulatory requirements, and scheduling norms. Office and administrative positions typically have relief factors of 1.10–1.20 (5–8 day coverage, low absence rates). Manufacturing and warehousing operations run 1.15–1.30 for 5-day operations and 4.5–5.0 for 24/7 continuous operations. These sectors have moderate absence rates but benefit from cross-training and flexible scheduling.
Healthcare facilities typically use relief factors of 5.0–5.8 for 24/7 nursing positions, reflecting higher absence rates (3.5–4.5%), mandatory training requirements, and regulatory staffing ratios that prevent running short. Oil and gas operations, particularly offshore platforms, use crew rotation factors of 2.0–2.2 for equal-time rotations (14 on/14 off) and 1.5–1.7 for hitch rotations (28 on/14 off). Mining operations on 12-hour schedules typically run 4.2–4.8.
Emergency services (fire, EMS) have some of the highest relief factors at 5.5–7.0, driven by 24-hour shift schedules, high training requirements, mandated fitness-for-duty programs, and above-average injury/sick leave rates. Process industry control rooms (refineries, chemical plants, power plants) typically target 5.0–5.5 for 12-hour rotating shifts with strict fatigue management rules (API RP 755) that limit overtime coverage options.
Headcount Coverage Calculator
Calculate minimum staffing for 24/7 operations using relief factor analysis. Accounts for PTO, sick leave, training, FMLA, and workers comp with rotation presets including DuPont and Pitman.
Rotation Patterns and Headcount
4-crew, 12-hour "DuPont" schedule: Four crews rotate through a pattern of day shifts, night shifts, and off-days over a 4-week cycle. Each crew works an average of 42 hours/week (alternating 36 and 48-hour weeks). Coverage requires exactly 4 crews (one on days, one on nights, two off at any given time). The base relief factor before absences is 4.0, but with a realistic absence budget, you need 4.4–4.8 FTEs per position, meaning a fifth "swing" or "utility" crew is common.
5-crew, 12-hour "Panama" or "2-2-3" schedule: Five crews rotate through a 2-on, 2-off, 3-on, 2-off, 2-on, 3-off pattern. Each crew averages 36.5 hours/week (alternating 36 and 48-hour weeks across a 2-week cycle). The fifth crew provides built-in relief coverage, resulting in lower overtime. The base relief factor is 5.0 before absences, with effective need of 4.8–5.2 FTEs per position depending on absence rates. This pattern is increasingly popular in process industries because it reduces chronic overtime.
3-crew, 8-hour "continental" schedule: Three crews cover 24 hours with 8-hour shifts (day, evening, night), typically on a 5-on, 2-off weekly rotation. Each crew works 40 hours/week. The base relief factor is 4.2 (168 hours/week ÷ 40 hours/crew), and with absences rises to 4.6–5.2. The advantage is no overtime built into the base schedule. The disadvantage is that 8-hour night shifts produce circadian disruption 5 days per week without the 3–4 day recovery blocks that 12-hour schedules provide.
Overtime as Planned Coverage
Some operations intentionally staff below the calculated relief factor and plan to cover the gap with overtime. This makes financial sense when the gap is small (less than 5–8 hours/week per position), the work is not safety-critical, and qualified workers are willing to pick up extra shifts. The cost of overtime for a small gap is often less than the fully loaded cost of an additional FTE who would otherwise have bench time.
The math: if your relief factor calculation shows you need 4.6 FTEs and you staff at 4, the gap is 0.6 FTE × 1,850 net hours = 1,110 hours of annual overtime. At a true overtime cost of 2.0–2.5× base (see the overtime cost guide), that equals roughly $66,600–$83,250 in overtime for a $30/hr worker. A fifth full-time employee costs approximately $84,240 fully loaded. The break-even is close, so the decision often comes down to non-financial factors: is coverage reliability critical? Are workers willing to do the OT? Is fatigue a safety concern?
The danger of this strategy is "overtime creep." A 0.6 FTE gap assumes average absences, but absences are lumpy—flu season, summer vacation peaks, and FMLA events can spike the gap to 1.0+ FTE for weeks at a time, forcing excessive overtime on the remaining crew. Build a Monte Carlo model (or at minimum, stress-test your staffing plan against your worst-absence quarter from the last 3 years) to ensure the plan survives real-world variability.
Overtime Cost Projection Tool
Analyze the true cost of overtime including hidden costs like turnover, fatigue incidents, FICA, and workers comp. Compares OT strategy vs hiring additional staff with break-even analysis.