How to use this calculator
- Enter or choose request date, appointment date (one pair per line).
- Enter or choose access target.
- The median lead time updates as you type. Use Copy result or Share to keep it.
Method
Lead time = Appointment date − Request date (calendar days); 90th percentile = value at rank ⌈0.9 × n⌉ (nearest-rank); Within target = count(lead time ≤ target) ÷ n
- n
- number of appointments
- Target
- maximum acceptable days to appointment
Worked example
- Lead times: 14, 3, 30 and 7 days; sorted 3, 7, 14, 30.
- Mean = 54 ÷ 4 = 13.5 days; median = (7 + 14) ÷ 2 = 10.5 days.
- 90th percentile: rank ⌈3.6⌉ = 4, which is 30 days; 3 of 4 within 14 days = 75%.
Half of these patients waited 10.5 days or less, but one in ten waited up to 30 days; 75% were seen within 14 days.
What the result means
The median shows the typical wait; the 90th percentile shows the long tail that patients complain about. A falling average with a rising 90th percentile means some patients are waiting longer.
Assumptions and limits
- Lead time is counted in calendar days, so a same-day appointment is 0 days.
- Every line is one completed or booked appointment.
- Does not separate patients who chose a later date from those offered no earlier slot.
- Third-next-available appointment, another common access measure, needs the booking calendar rather than completed appointments.
Questions
Why is the median the headline figure?
Waiting times are skewed by a few very long waits, which pull the average up. The median is the wait that half of patients beat.
Should weekends count?
This calculator counts calendar days, as patients experience them. Use the same convention every time you report.