Article — 120 Day Calculator
What is 120 days from today? The 120 day calculator explained
120 calendar days equals 17 weeks and 1 day, or approximately 3.94 months at the Gregorian average. 120 business days, by contrast, runs about 168 calendar days (24 work weeks). The 120 day calculator at the top of this page resolves both kinds — forward or backward — with weekday output.
The number 120 shows up in surprisingly many places: US student visa rules, civil-procedure deadlines, employment probation contracts, extended retail return policies, and the long tail of NET 120 invoice terms. Knowing the precise date matters because "four months" is almost — but not exactly — 120 days, and the off-by-one can break a legal filing.
What the 120 day calculator does
The 120 day calculator takes a start date and returns the date that falls 120 days before or after it. The choice between calendar days and business days matters: 120 calendar days is just over four months end-to-end, while 120 business days (Monday through Friday only) spans about 24 weeks of working time, or 168 calendar days from start to finish.
The output also shows the weekday, which matters in legal contexts where deadlines that fall on a weekend roll forward to the next business day. US federal courts and the IRS apply this rollover automatically; most private contracts do not.
Florida Civil Procedure Rule 1.070(j) requires that a summons be served on the defendant within 120 days of filing the complaint. Failure to serve within the window can result in dismissal of the case without prejudice. The 120-day clock starts the day the complaint is filed and runs as calendar days, not business days.
120 days in weeks, months, and hours
120 days breaks down cleanly into 17 weeks and 1 extra day. In hours, that is 2,880 hours, or 172,800 minutes if you ever need that level of resolution. In Gregorian months it is approximately 3.94 months — close enough to four months that the two are often used interchangeably, although they are not the same.
The exact "month" length used here is 30.436875 days, which is the Gregorian year (365.2425 days) divided by 12. Four calendar months can be anywhere from 120 days (February through May in a non-leap year) to 123 days (most four-month spans containing back-to-back 31-day months). The 120 day calculator avoids the ambiguity by counting actual calendar days.
- 17 weeks + 1 day = exactly 120 calendar days
- 3.94 months at the 30.44-day Gregorian average
- 2,880 hours in 120 days end-to-end
- 168 calendar days = 120 business days (Mon-Fri only)
- ~32.9% of a 365-day year
- 24 work weeks at the standard 5-day schedule
Calendar vs. business 120 days
The most common source of confusion in the 120 day calculator is whether the deadline counts calendar days or business days. Calendar days include weekends and holidays. Business days exclude Saturday and Sunday, and in some legal contexts also exclude federal holidays.
The two diverge fast. 120 calendar days runs from, say, January 1 to May 1. 120 business days from the same start runs to roughly June 18 — about seven extra weeks. Read the contract or statute carefully before assuming which one applies.
The 120 day rule for US visas
The most-searched 120-day rule involves US student visas. F-1 and M-1 visas can be issued by a US consulate up to 120 days before the program start date listed on Form I-20. The visa stamp can sit in a passport for the full 120-day window before classes begin, giving consular sections enough lead time to process applications during peak admission cycles.
The 120 day rule does not extend to entry: the Department of Homeland Security only permits arrival in the United States within the 30 days before the program start date. Arriving on day 120 is not permitted; the visa just exists earlier so it is ready when needed.
The F-1 120-day rule applies to visa issuance, not to US entry. A student whose program starts September 1 can apply for and receive the visa as early as May 4, but cannot enter the United States until August 2 (30 days before program start). Treating the two windows as the same has resulted in turn-arounds at US ports of entry.
120 days in employment and probation law
120-day probationary periods are common in US private-sector employment contracts. The contract usually specifies whether the count is calendar days or working days — a distinction that adds nearly two months to the actual end date when the answer is working days. Federal Senior Executive Service appointments use a one-year probationary period instead.
Some state employment laws also reference 120 days for unemployment benefit eligibility, layoff notice requirements (especially for mass layoffs under WARN Act variants), and reinstatement rights for employees returning from protected leave. Always anchor the count to a specific start date — the day employment began, the day notice was given, or the day leave commenced.
120 days in court filings and contracts
Florida Rule 1.070(j) is the best-known 120-day court rule, but several states use a similar window for service of process. The 120-day clock starts at filing and runs as calendar days. Other 120-day contract contexts include NET 120 invoices (long payment terms used in heavy industry and government supplier contracts), 120-day grace periods for some insurance products, and 120-day cure periods in commercial real-estate lease disputes.
120 days 17 weeks + 1 day120 days 3.94 months120 business days 168 calendar days120 days backward start - 120120 days ≈ 4 months shorthand onlyUsing the 120 day calculator correctly
Three settings matter. First, the start date — defaults to today but accepts any past or future date. Second, direction — "from" adds 120 days, "before" subtracts. Third, day type — calendar or business. The 120 day calculator returns the target date plus its weekday, since weekday matters for legal deadline rollover.
For any 120-day legal deadline, write down both the calendar-day target and the next-business-day rollover target. If the target lands on a Saturday or Sunday, courts and tax authorities usually apply the rollover; private contracts usually do not.
Common 120 day calculator mistakes
Three errors come up repeatedly. First, treating "120 days" and "4 months" as equivalent — they are off by one to three days. Second, mixing calendar and business days — a 120-day window can end nearly two months later when business days are intended. Third, forgetting weekend rollover in legal contexts: if a 120-day deadline lands on a Sunday and the court applies rollover, the actual deadline is the following Monday.
The 120 day calculator at the top of this page handles all three correctly when configured. The output shows the weekday explicitly, so any rollover handling is a one-look decision rather than a separate calculation.