It is difficult to predict 800m times, based on what you can do for other distances, with any degree of accuracy!
It is much easier to compare times across 1500m thru marathon, because these distances are predominantly endurance events.
It is also easier to compare times across 100m thru 400m, as these distances are predominantly strength events.
The 800m is a unique mix of strength, endurance (aerobic capacity), and anaerobic capacity.
The 400m is also partly anaerobic, particularly for us slower Masters athletes.
There are various Time Predictors around, and they tend to give wildly different results.
For example, take a look at http://run-down.com/statistics/calc.php, which compares various predictors. Their "average" column might be a good as any.
Even thinking about whether improvements in one distance will carry over into improvements in another distance, one must know how specific your training is.
Some training carries over. Some doesn’t. Training which improves you for one distance may have little or no affect on other distances.
As a rule then, there are three possible sets of distances one can specifically be training for at a given time.
(a) 100m to 400m
(c) 1500m and above.
Even then, specific 400m training can compromise the 100/200.
And for elite senior athletes, the 1500m might be grouped with the 800m rather than grouped with longer distances, again because we are not elite senior athletes.
Our non-elite masters training group will focus on strength (hill work) and anaerobic training (interval work with short recovery) for the next six weeks.
But do check out http://run-down.com/statistics/calc.php to see what you might be capable of.
O’Keefe Rail Trail
11 hours ago