Your strongest argument is the "related to or useful in" language โ a cooking recipe app has no connection to fintech. However, employers sometimes argue broadly:
- "You used software development skills you refined at our company"
- "The app uses similar technology stack/architecture as our products"
- "Any software development is 'useful' to a technology company"
These are generally losing arguments, but the strength of your position depends on your state:
California (Labor Code ยง 2870): Explicitly protects employee inventions developed entirely on personal time, with personal resources, that don't relate to the employer's business. Your recipe app would be protected.
Other states: 8 states have similar statutes (DE, IL, MN, NC, WA, KS, UT, MT). In states without such laws, the contract language controls more heavily.
Regardless: did you use ANY company resources? Company laptop, company email, company cloud accounts, any work time? If yes, that weakens your position. If you can demonstrate complete separation (personal devices, personal time, unrelated field), you're in a strong position.