If you were paying attention you would have seen that I predicted a 22:59 for the 5k this past Saturday. My actual time was 22:59. Now that was closer than I could have ever expected but it's pretty normal for me to be able to predict my race times based on my current condition. The are several race pace calculators out there and they are quite useful but are dependent on you having run another recent race close to the same distance as the one you are about to run. And they can't take into account the training you have done in between and whether you have been injured or had a layoff for a long period of time for whatever reason.
A few years ago I came up with a workout I do before racing a 5k that serves as a good last bit of speedwork to sharpen just before a race and has also proven to be a very good prediction tool.
So, if you want to try it get to a track although it can be done on a flat greenway, just not as precise. The workout should ideally be done 4 days out from the event but anytime within 3 to 5 days will do.
I began with a warmup mile and then take a 2 minute rest.
Then I run mile at what I have reasonably determined to be my goal pace. If at anytime during this mile it becomes difficult then the goal is too lofty. So back off until you feel like you could hold that pace for a lot longer. ( my mile was 7:26). Then rest 2 minutes.
Next run 1/2 mile at a pace that is about 15 seconds per mile faster than the mile.. This will simulate the middle of the race. It should feel hard but still something in the tank. If you can't hold the pace or struggle then again, you have over estimated your current condition. ( I ran 3:35 or 7:10 pace. Dead on what I needed.) Then rest 2 minutes.
Now run 1/4 mile at about 15 to 20 seconds per mile pace than the half. This simulates the last mile. It will hurt but you shouldn't get to the end with your hands on your knees just yet. Rest 1 minute and then do another 1/4 mile at about the same pace but kick it in the last 100 meters. Now you can gasp.( I needed to run about 1:42 to 1:43. Ran 1:41 and 1:40)
That's it. If you nailed the workout then the 1st mile should be your goal give or take a couple of seconds per mile. If you struggled a bit toward the end back off the goal a little and maybe you will have a good day. If you are strong at the end as I was then expect to be a little faster. on race day.
My workout suggested about a 23:15. Since I felt good and the conditions were favorable I had a strong feeling I could crack 23. And my first mile on race day? 7:27 Average for race 7:23.
I've done this before all but one 5k since 2014 and it has always been within a few seconds. Of course you also have to take into account the course and weather conditions. If it's hilly that will add seconds per mile and if some unusual weather crops up in a few days that too can make you change the goal. This is where lots of experience and knowing your body come in.
This was put to the test last Feb. before the Run for the Roses. My predictor showed a 6:59 pace but I knew it was a very tough hilly course so I was expecting about a 22:30 or about a 7:15pace. Then on race day we had freaky weather. The normal temps I had running in were in the 30's and 40's but on race day it was 80F at the start. It's a short race but I still knew to expect it to make it harder to breath and so I predicted just before we started a 22:45. Actual was 22:43.