Many folk who have completed C25K talk about completing 5k. Would they know unless they were on a running machine or own a Fitbit? I'm speaking from my own experience. I wasn't unfit at the start, or overweight, but at the end found the 30 mins was only 4k.
Running 5k: Many folk who have completed C25K... - Couch to 5K
Running 5k
Either a treadmill or if outdoors then a device with GPS (sat nav tech).
That device could be a smartphone running a dedicated app or a running watch (eg Garmin) or a health/lifestyle wristband like a Fitbit.
Like John said 😬
I use Strava on my phone, and didn't measure any distance until I'd completed C25K, i.e. three x 30 minute runs.
That said I'm now planning to treat myself to a running watch
There are lots of low tech ways of checking distance covered such as measuring on a map.
People undertaking C25k have a vast range of abilities/disabilities, age, fitness and natural talent and the distance covered at graduation has more to do what you bring to W1R1 than any magic that C25k endows upon graduates.
I bet you weren't able to run 4k before the plan and you are so much nearer the 5k now.......congratulations.
Have you read the guide to post C25k running? healthunlocked.com/couchto5... it is full of tips.