I've spent the evening today trying to calculate some dates for my lore-rich TES fan fiction tale. I need to be able to quickly and easily work out things like....

1. Given a start date, what will the new date be after so many years?
2. How many years have elapsed between a start and end date?
3. What was the start date, if it was so many years before a known date?

I'm currently only working at a year level, but it may at some time be necessary to calculate months, or even days. Rather than trying to manually calculate these, I figured I must be able to use my computer to do this automatically. The calendar of the Elder Scrolls is not as straight-forward as our real-world calendar. There were 2920 years in the First Era, 896 years in the Second Era, and 433 years in the Third Era. Trying to calculate anything in the Merethic or Mythic Eras is pretty much impossible, so I just lump them together as "pre history" if my calculations stray that far back.

Existing Solutions?

What I'm wondering is if there is already a calculator out there somewhere that can do these type of date manipulations for me? No doubt other people would find such a tool useful, particularly loremasters and fan fiction writers. If someone can point me to an online calculator or similar, it would sure save me a lot of time.

Spreadsheet Solution

I have made a start on a spreadsheet in LibreOffice to perform these calculations. So far I think I have the first and second problems (as itemized above) sorted, and I'm still working on the algorithms for the third problem, (subtracting years from a given date). I'd really like to test my work with some examples that people here can throw at me, if that is okay. If people could submit a question that I can put into my spreadsheet, it would be really helpful. Below are a couple of examples....

• How old was Tiber Septim at his death? (Given he is believed to have been born in 2E 828, and died in 3E 38, according to http://www.uesp.net/wiki/Lore:Tiber_Septim). My answer: 934 years.
• If Arngeir was 300 years old in 4E 201 (total speculation here), when would he have been born? My answer: 3E 334.

Java/Javascript Solution

If I can get my spreadsheet working accurately, I might consider coding this in Java or Javascript. Once again, if this already exists out there on the Internet somewhere, then I'd prefer not to reinvent the wheel. If it doesn't exist, would others find such a tool useful? Would it be worth my while coding it? I'm keen on open-source software and would not be making anything out of it, not even from advertising. I'd be happy to collaborate on such a project, too. I'm not a great programmer, but I can struggle along on my own.

Any feedback, advice, examples to try out in my spreadsheet, or links to existing solutions would be most welcome.

Don't know, but perhaps Appendix II of the http://www.gamesas.com/topic/1461523-the-new-encyclopedia-tamrielica/ might be of help?