This is another project that’s been on my to do list for too long. Back in early 2024, I built an age grade calculator that calculated actual age grades for marathon performances along with a runner’s position (percentile) within the distribution of all finish times for their age group.
I updated that calculator in early 2025 with new data, but I never got around to updating it at the start of this year. Like the race pace comparison tool, I had also built this calculator in Streamlit. It made it quick and easy to do the backend in Python, which I’m familiar with. But it left something to be desired with the front end – and the hosting wasn’t all that reliable.
This week, I updated the data to include new results from 2025 and to calculate actual age grades using the new 2025 age factors. I also rebuilt both the backend and the frontend, creating an app that’s a more elegant and reliable solution.
I also added the ability to compare up to five runners from different age groups. And I added a graph to show the full distribution of finish times – instead of just displaying the percentile of where a particular performance ranked.
Check out the new age grade calculator here. And if you’ve got other suggestions or requests for something similar, let me know. I’m always looking for ways to make this data more useful for people – other than just projecting the Boston cutoff time.
Here’s a screenshot of the results from the new calculator, with the graph included.