Biweekly means every two weeks on the same weekday — 26 paydays in a typical year, occasionally 27. Semi-monthly means twice a calendar month on fixed dates, usually the 15th and the last day — always exactly 24 paydays, on whatever weekday those dates happen to fall.
They are not interchangeable. Biweekly periods always cover exactly two full workweeks. Semi-monthly periods cut through the middle of workweeks, and that one fact causes nearly every problem new employers hit.
The real difference is where the period ends
Overtime under the Fair Labor Standards Act is calculated on a workweek basis — a fixed, regularly recurring 168-hour period. It need not match the calendar week, but once you set it, it stands. Hours are never averaged across two weeks or tallied per pay period.
With biweekly payroll, the pay period is two clean workweeks. Overtime falls out of the math naturally.
With semi-monthly payroll, a period like the 1st through the 15th holds partial workweeks on both ends. You still owe overtime per workweek, which means splitting hours across the boundary and often paying overtime on a check whose period shows only part of that week. Done by hand, this is where employers underpay people without meaning to.
The rule of thumb: if you have hourly, nonexempt employees, run biweekly or weekly. If everyone is salaried and exempt, semi-monthly is clean and gives you two fewer payroll runs a year.
What changes in the numbers
For a salaried employee, annual pay is identical either way. Only the slicing changes:
- Semi-monthly: annual salary ÷ 24. Larger checks, same amount every time.
- Biweekly: annual salary ÷ 26. Checks are about 7.7% smaller, but there are two more of them.
Benefit deductions are the practical headache. Premiums are usually quoted monthly, which divides evenly into 24 semi-monthly periods. On biweekly, employers either spread the annual premium over 24 of the 26 checks and skip the two "third paycheck" months, or divide by 26 and take a smaller bite each time. Pick one, document it, and tell employees which months are skipped.
Exempt-employee salary tests translate by period too. 29 CFR 541.600 sets the federal minimum salary for the executive, administrative, and professional exemptions as a weekly figure and gives the equivalents. As of August 2026 it reads $684 per week, or $1,368 biweekly and $1,482 semimonthly — the 2019 levels, which the Department of Labor restored to the regulation by technical amendment in May 2026 after courts vacated the 2024 increase.
The same section says the shortest qualifying period of payment is one week, so you cannot stretch a thin salary over a longer period to clear the bar. And these numbers move: several states set higher thresholds that rise annually. Check the current regulation and your state labor department before relying on any figure, including this one.
The 27-paycheck year
Every so often a biweekly calendar produces 27 paydays — when the year contains 53 of your payday's weekday and your cycle lands on the first one.
2027 is one of those years for Friday payrolls. January 1 and December 31, 2027 are both Fridays. If your biweekly paydays fall on January 1, you will issue 27 checks that year. Start the cycle a week later and you are back to 26.
Two legitimate responses:
- Do nothing. Salaried staff get one extra period of pay. Employees like it, but it is a real budget line — accrue for it in advance.
- Recalculate. Divide annual salary by 27 for that year so total pay is unchanged. Legal, but it looks like a pay cut on every check. Announce it early and in writing, and confirm it does not push an exempt employee below the weekly salary floor.
Semi-monthly payroll never has this problem. It is 24 periods, forever.
Pay frequency is a state-law question
Federal law does not dictate how often you pay people. States do, and the rules are specific.
- New York: manual workers must be paid weekly, within seven calendar days of the end of the week in which the wages were earned. Clerical and other workers, at least semi-monthly. Employers averaging 1,000 or more employees in the state can apply to the Commissioner of Labor to pay manual workers less often, but never less than semi-monthly.
- California: Labor Code § 204 requires wages twice a month. Work performed the 1st–15th is due between the 16th and 26th; the 16th through month-end is due between the 1st and 10th of the following month. Weekly, biweekly, and semimonthly payrolls satisfy the section if wages are paid within seven calendar days of the period's close.
- A few states have no general private-sector pay-frequency statute at all. The U.S. Department of Labor keeps a state-by-state table of payday requirements.
Semi-monthly satisfies most "twice a month" rules. Biweekly usually does too, but not always — read your state's text.
Changing frequency can trigger notice duties. New York Labor Law § 195(2) requires written notice at least seven calendar days before a change to pay rate or payday, unless the change appears on the wage statement.
If you are switching
- Confirm the new schedule is legal in every state where you have employees.
- Give written notice before the change, not after.
- Never delay wages already earned to bridge the gap. Run a short transition period and pay it on time.
- Re-time benefit deductions and any garnishments, which often carry per-period math of their own.
- Update withholding. IRS Publication 15-T publishes separate tables by payroll period — weekly, biweekly, semimonthly, monthly — and is reissued every year, so use the current edition.
- Your federal deposit schedule comes from the lookback-period rule in Publication 15 (Circular E), not from how often you pay people. Changing frequency does not move your deposit deadlines.
What employees should check
Read the period dates on the stub, not just the amount. Hours should be broken out so you can tie them back to actual workweeks, especially on semi-monthly checks. If a stub shows 88 hours with no overtime line and you know you worked past 40 in one of those weeks, ask.
If you produce pay statements yourself, what matters is getting the period boundaries and the hour breakdown right. UWageCo prepares statements from the figures you enter; every document carries a disclosure that the data was customer-supplied and not independently verified. It prepares documents only — anything going to a tax authority is filed by you or your accountant.
This is general information, not legal or tax advice. For your situation, talk to a payroll professional or an employment attorney, or your state labor department.