For appointments booked on the day the 'did not attend' (DNA) rate for practices in England is just 1.9%, compared with 5% for appointments booked a day in advance - 2.6 times higher.
Analysis of data from NHS Digital reveals that the further ahead patients book appointments, the more likely they are to fail to attend.
For appointments booked 2-7 days ahead, the DNA rate rises sharply to 6.8% - and for appointments booked more than a week ahead the DNA rate ranges from 8.2% to 8.9%.
GPonline revealed last week that patients fail to attend an estimated 16.4m appointments a year - 5.34% of all appointments booked with GPs or other practice staff - equivalent to the annual output of 375 average GP practices.
The latest findings - from analysis of NHS Digital data by data scientist Stephen Black - suggest that switching to models that make a greater number of consultations available for booking on the day could bring down DNA rates by a significant margin - and help practices boost capacity at a time when many are struggling to cope with heavy workload.
If all of the 307.4m GP appointments GP practices deliver every year were booked on the day, the figures suggest that just 5.8m would be missed - potentially making more than 10m additional appointments available every year. This is equivalent to more than 1,500 GP appointments for every practice in England.
DNA rates
Mr Black told GPonline he had been surprised by how clear the link was between DNA rates and how far ahead appointments were booked. 'This suggests there could be a really big benefit for the system of offering same-day appointments,' he said.
'It creates a big increase in the capacity of general practice to see patients if most of them turn up - losing such a large proportion of the capacity of the system is a big incentive to do same-day appointments.'
GPC chair Dr Richard Vautrey said practices had to strike a 'difficult balance' between a responsive service and demand on the day, and patients wanting to book ahead.
He said it was not unreasonable for patients to want to book ahead when they needed to return to the practice for a review at a certain time, or wanted to see a particular doctor.
Workload
Dr Vautrey said that many practices probably schedule a greater proportion of same-day appointments on a Monday, when they are at their busiest, to benefit from the lower DNA rate this brings.
However, Harry Longman, chief executive of GP Access - a company that helps practices reorganise their workflow to improve patient access - said DNAs were a 'symptom of a poorly performing system'.
The national DNA data mirror findings from smaller studies that have underpinned his company's approach, he said.
'The traditional view has been that DNAs are a huge problem, and something must be done - but what? Practices have put notices on the wall in reception about how bad it is, and the cost of missed appointments; they have tried SMS messages. These approaches have some effect.
'We take a different view. Looking at data on the elapsed days between making the appointment and the booking, I did a study on 800,000 appointments that found DNAs on day one were at 1%, day two 3% and it climbs from there to around 5% or 6% for bookings further ahead.'
DNAs were not a problem with patients, but with the system practices used, Mr Longman argued.
'So how do you get DNAs down to 1%? Book on the same day - don't make people wait.'
