How this calculator works
One hundred twenty days is a common notice period and a natural four-month planning block. The calculator moves by 120 whole calendar days rather than four calendar months, and the two can differ by a day or two because months are 28 to 31 days. The month-start table is useful for comparing several possible notice dates, and the weekdays-inside count gives the working days involved before holidays.
Formula
result = fromOrdinal(O(start date) + 120) forward, or fromOrdinal(O(start date) - 120) backward. The span is 17 weeks and 1 day. Weekdays inside counts Monday to Friday dates after the earlier endpoint through the later endpoint.
Worked example
120 days after 2026-11-01 is 2027-03-01, a Monday, 17 weeks and 1 day later with 86 weekdays inside. 120 days before 2026-11-01 is 2026-07-04, a Saturday.
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Frequently asked questions
Is 120 days four months?
Approximately. Four months are 120 to 123 days depending on which months are covered, because February is shorter than the rest. When a contract says four months, the month counter is the more faithful tool.
What are common 120-day notice periods?
Landlord, employment and contract notice periods sometimes use 120 days because it is a clear four-month block. Whether the notice must be received on or before the date, and whether it runs from the notice date or the day after, changes the deadline.
Why is the weekday shown separately?
A deadline that falls on a weekend or statutory holiday may move under the applicable rules. Seeing the weekday lets you check whether a mailed notice should be sent a day or two earlier.