The stardate system used in the Banshee Squadron stories is very simple and straightforward - no 'stardate calculator' program is required. Any fictitious date system that isn't comprehensible without a computer program is utterly meaningless to the reader anyway.
Here is how to interpret Stardates. The system is a continuation of the system invented by the producers of TNG, which was as follows:
- The first digit was a '4'.
- The second digit was the season number.
- The last 3 digits and the decimal were semi-sequential made-up numbers starting with low numbers early in the season and working progressively higher as the episodes went on.
Therefore, the stardates for TNG Season 1 looked like 41xxx.x. Season 2 was 42xxx.x, and so on until 49xxx.x was reached. The next year was stardate 50xxx.x, and so on.