In Montana, your final paycheck is due immediately (within 4 hours or by end of the business day; a written policy can extend this to the next payday or 15 days) if you are fired, and next scheduled payday or within 15 days, whichever is first if you quit.
Final paycheck deadline in Montana
If you are fired or laid off
Immediately (within 4 hours or by end of the business day; a written policy can extend this to the next payday or 15 days)
If you quit
Next scheduled payday or within 15 days, whichever is first
What your final pay must include
Your final paycheck must include all the wages you earned through your last day. Whether it also has to include unused vacation depends on your state and your employer's policy, some states treat accrued vacation as wages that must be paid out. See Montana PTO payout rules. If an employer misses the deadline, many states add penalties. This is general information, not legal advice.