The three common accrual methods
Employers grant paid time off in one of three ways. Per pay period is the most common: the annual allowance is divided by the number of paychecks and credited each payday, so the balance steps up 26 times a year for a biweekly employee. Per hour worked suits hourly and part-time staff, because the rate is the annual allowance divided by the annual scheduled hours and someone who works fewer hours earns proportionally less. An annual lump grant drops the whole allowance into the balance on a fixed date, typically January 1 or the work anniversary, which is generous early in the year and creates a liability the employer has to manage.
This calculator converts days into hours first, using your scheduled hours per week divided by five to get a standard workday. Ten days at 40 hours a week is 80 hours; at 30 hours a week the same ten days is only 60 hours, which is why PTO policies are almost always written in hours.
Worked example
Take an employee granted 15 PTO days a year on a 40-hour schedule, paid biweekly, starting the year with a 40-hour balance. Fifteen days at eight hours is 120 hours a year. Divided by 26 paychecks, that is 4.615 hours credited every other Friday, or about 0.577 hours for every hour worked if the employer uses the hourly method. From January 1 to June 30 is 181 days, which is 12 completed biweekly periods, so 55.38 hours accrue. Added to the opening 40 hours, the balance on June 30 is 95.38 hours, which is 11.92 days or roughly two and a half weeks of time off. A 240-hour cap is nowhere near being hit, so nothing is forfeited.
Caps, carryover and the law
Most policies limit how much can build up, either as a hard accrual cap that stops you earning once the balance is reached or as a year-end carryover limit that wipes out the excess. The calculator applies a simple maximum balance and tells you how many hours would be lost. Caps matter most for people who rarely take time off, because hitting one means working for free.
There is no federal law requiring any paid vacation at all. The Fair Labor Standards Act covers wages and overtime, not time off, so the amount, the accrual method and the carryover rules come entirely from the employer's policy or a union contract. State law can add to that picture: more than a dozen states and many cities mandate paid sick leave, and states including California, Colorado, Montana and Nebraska treat accrued vacation as earned wages that must be paid out when employment ends and cannot simply expire under a use-it-or-lose-it rule. Check your handbook, since sick leave and vacation are often tracked separately even when the company calls the whole thing PTO.