I wrote a little program to work it all out. I’ll share as Solar first got me onto this and its remarkably accurate. I believe it was a french guy developed the concept of SDI.
SDI = Log (T1/T2) / Log (D1/D2)
Where times are expressed in seconds, distances in meters
To predict a time
T1 * (DP/D1) ^ SDI
Where DP = Distance you wish to predict time for. so I’d typically use the 100 time as base here
The 1.06 average decay was based on a study by a guy called Pete Riegel
THAT IS INCREDIBLE!!!
That’s going into my training spreadsheet 
Although my 1900m time was quicker this year 
For the lazy - copy the layout below:
C2, C3, D2 and D3 are your inputs.
C5 = LOG((D2*86400)/(D3*86400))/LOG(C2/C3)
D8 =(($D$2*86400)*POWER((C8/$C$2),$C$5))/86400
Then just drag D8 down.
Oooooh, I love a good spreadsheet 
Can I just check my understanding of this? Are the times/distances your PB’s for those distances as when you perform a CSS test, the 200m is somewhat fatigued from the 400? Thanks
typically in swimming we would use pb’s, well recent fast times, but to be fair as long as conditions are reasonably similar it shouldn’t matter too much. If you look at Poets CSS times I recon there’s not much in it. it would be a few seconds at most either way.
this could be because of the times testing with are CSS test do maybe your 400 is a bit slower than it could have been or your pacing meant you held back a bit much or died a bit in last 100. Also was thw 1900 OW, so not quite 1900? Do a 100 flat out also in the pool. maybe use the 100 and your best 400 or even the 1900 to see what you get
Cheers coach @Hammerer
I was gonna try for a 200PB today 
(all PBs are non diving, start from the shallow end)
I think the Cotswold 113 was pretty accurate - people I swam with clocked it at 1850-1980.
Either way, that calculator is pretty damn impressive!
Certainly more so than the running ones 
Thanks, agree there wouldn’t be much in it.
I plugged your formulas into my CSS sheet for comparison.
I have a little java applet i wrote for it, typical developer should have just used excel! I have a second column with TFD times in and a 3rd column with difference in seconds
| Distance | Predicted Time (SDI=1.09) | Target Prediction (TFD=1.06) | EI |
|---|---|---|---|
| 100m | 0:01:16 (0:01:16) | 0:01:17 (0:01:17) | +0:00:02 |
| 200m | 0:02:41 (0:01:21) | 0:02:41 (0:01:21) | -0:00:00 |
| 400m | 0:05:43 (0:01:26) | 0:05:36 (0:01:24) | -0:00:07 |
| 500m | 0:07:18 (0:01:28) | 0:07:05 (0:01:25) | -0:00:12 |
| 750m | 0:11:21 (0:01:31) | 0:10:54 (0:01:27) | -0:00:27 |
| 800m | 0:12:11 (0:01:31) | 0:11:40 (0:01:27) | -0:00:31 |
| 1000m | 0:15:32 (0:01:33) | 0:14:47 (0:01:29) | -0:00:46 |
| 1500m | 0:24:11 (0:01:37) | 0:22:43 (0:01:31) | -0:01:28 |
| 1900m | 0:31:18 (0:01:39) | 0:29:11 (0:01:32) | -0:02:07 |
| 3800m | 1:06:41 (0:01:45) | 1:00:50 (0:01:36) | -0:05:51 |
| 5000m | 1:29:57 (0:01:48) | 1:21:23 (0:01:38) | -0:08:35 |
| 10000m | 3:11:39 (0:01:55) | 2:49:40 (0:01:42) | -0:21:59 |
I am not going to swim 5 or 10km, you sadist 
I like that TFD column and the difference.
Really shows how far you’re out and where it starts to go wrong fast!
I was toying with writing a quick Python web App and throwing it up on Heroku, so you could all access it…but I’m “busy” 
The one written by @arhy is still up and running: http://arhy.org/files/estswimtimes.html
ETA: it doesn’t go up beyond 3.8km (for headcases)
Edited (again) to leave the URL as text to see if you can just copy it into a browser.
My 200 and 400m times from last week were both within 1s of yours… so I guess my CSS must be similar, around 1:42, I’ve not done a CSS test for 2 years, and it was 1:53 back then.
I also used the formula to create my own sheet, so looks like my estimated IM time is 1:10, so still need to work quite a bit to get that down lower
Not for me… ?
Just got back from the pool, broke my old 50m non-diving PB twice
(35.4, then 34.3! , old PB was 36s)
Then broke my 100m LTS PB of 1:17 with a 1:16
I failed to break the 200, as I was pretty spent by then 
closed the session out with some drills.
Edited so copy and paste might work.
Cheers - that’s mint!
Looks like a 28 minute 1.9km could be on the cards, though I’m not sure my precious moist skin can take too much more chlorine!
I know from your cycling and running performances that you’re way, way (and a few more ways) fitter than me so that would suggest to me that there’s still something technical to be found as you’re not seeing the benefit of that extra fitness in your swim.
bloody show off, better than mine. I feel an edit coming on but Im keeping the 5 and 10k times 
It’s not mine, I just took it from the 100m Vs Oly thread on TT 1.0. I have taken all the chat out and condensed that thread, it is
I did that at the time. Must try and find it see if there is anything from solar I can use