Enter $100k as the startup salary, and zero equity (0 shares, $0 strike price, no funding round, any sale price for the liquidity event happening after 12 months).
Enter $150k as the big co salary, and the default 5.75% rate of return.
The result should be Total Big Co Earnings = $152,875 ($2,875 is the interest gained on the $50k salary diff for 12 months), but instead it shows $196,947!
Here's the calculation. It's a little high because we should be getting 1/12th of the 50k per month and compounding, but I'm assuming we got the full 50k up front and got a 5.75% interest compounded per month.
50000*(1.0575 ^ 12)
97799.02314394798212000000
edit 2: The bug is in this function and the one below it: https://github.com/vijedi/equity_calculator/blob/master/js/a...
If your interest rate is zero, the calculated interest is 11 * the monthly difference. Then it's added to your base big company salary, which is clearly wrong. It should be 12 * the monthly difference added to the startup salary.
edit 3: Opened a pull request with what I think is the fix: https://github.com/vijedi/equity_calculator/pull/4
Edit: Search http://www.tejusparikh.com/projects/equity_calculator/js/app... for bigCoInterest.