Does anyone have a formula to calculate their 60m time from their 50m time?
Yes, take your 50m time and add the amount of time if would take you to go from 50m to 60m 
Do you have a split on the last 20?
Really depends on your ability to run and hold top speed.
Nevertheless, multiply your 50m by 1.152 to 1.156 and you should get your potential time if top speed skill is sufficient.
This is based on following data. For example, in 1987 Ben Johnson ran 6.38 for 60m and 5.53 for 50m for ratio of 1.153
Lewis ran 6.50 and 5.64 for 1.152
Also in 1987 womens 100m, Issajanko ran 7.05 and 6.10 for 1.155
Phipps ran 7.53 and 6.48 for 1.16
Green in 1999 ran 6.39 and 5.55 for 1.152
Flo Jo in 1988 for ratio of 6.89 and 5.97 for 1.154
f.y.i. 55 to 60 meter conversion is .46 for those who did not know.
Spartacus, that assumes FAT of course.
When using the formula in training times, remember to add in your normal training to FAT factor. e.g., I always add 0.5.
That conversion is ridiculous to apply to everyone, assuming top speed is reached at that part of the race a 10.75 or so sprinter reaches that top speed, which is .92s per 10m. A 10.00 sprinter splits a .86 +/- .2 or so if you analyze splits. An 11.50 probably splits around 1sec per 10 meters at top speed (which is .5 for 55 to 60). Then as spartacus pointed out also include the ability of each sprinter to hold his speed and the 55 to 60 meter split could be top speed for a sprinter but a 5% decrease in speed compared to top speed for another. Do I like to complicate things or what. 
The most accurate way is get a video camera and see how many frames it takes during those 10m. if not try to calculate your athletes’ top speed per 10m. and add that to the 50m. time.
Well that conversion is what the NCAA uses for 55-60 meter conversion if you were to qualify for NCAA’S in that event. If it is so rediculous then why do they use it? Also i can tell you personally it is pretty close as i have run 6.63 and 7.12.
dcw23
Yes, I have calculated the data in regard to FAT figures.
“Well that conversion is what the NCAA uses for 55-60 meter conversion if you were to qualify for NCAA’S in that event. If it is so rediculous then why do they use it?”
It’s about right for someone who is just fast enough to qualify for NCAAs; that’s why they use it. For someone who is significantly slower or faster it would be quite useless.
Regards,
Robin.