This discussion has many people confused: do you go out and negative split the run, or do you get time in the bank early?
Here is what I recommend for most folks that have met critical volume for their event:
Olympic: 1st mile @ goal pace minus 7 seconds
Half: 1st mile @ goal pace minus 15 seconds
Full: 1st mile @ goal pace minus 30 seconds
The reason I use these baselines is that you routinely see the best run splits in IM drift no more than 1 minute from the 1st mile to the last. An example is if you have the ability to average 8:00 M/M for your race, run the first mile at 7:30 and drift no more than 1 minute to the last mile. Your goal pace should be that determined from the calculator which already takes into account durability and gives you a realistic expectation. The reason many people go out way too fast is that they may have great speed potential (great 5k times), but lack durability through volume and therefore the early pace feels easy but the lack of durability catches up with them later in the day and they lose serious time. They’d be much better off accounting for their lack of durability and pacing it accordingly from the start.
The reason I recommend heading out faster than the average race pace versus even or negative splitting like a straight running race is that you already have a significant amount of peripheral damage from the bike that will compound during the run and slow you down later on no matter what pace you head out at. This peripheral damage is less at shorter race distances and is the reason why the recommendation gets closer to even splitting the race at those distances.
For folks that have not met critical volume, I typically recommend 5-15 second walk breaks every 2 miles right from the beginning of the race. Their run pace should still use the above protocol but also factor in the time for the walk breaks.