January 1, 2026 to December 31, 2026 is 364 days, because the count measures the full days between the two dates rather than counting both endpoints.
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A contract that says 30 days and one that says one month can point to different dates, sometimes by a day or two, sometimes by more. Thirty days is a fixed count. A calendar month runs anywhere from 28 to 31 days depending on which month you land in. This tool counts days; for a month-based deadline, count to the same date number in the later month instead.
Every date here becomes a single number first, a count of days from a fixed reference point, so subtracting one from the other gives the gap directly without ever touching "how many days does this month have" as a separate step. That's what quietly handles the awkward part of date arithmetic: months running 28 to 31 days, and February picking up an extra one in leap years.
| Span | Days | Notes |
|---|---|---|
| One common year | 365 | February has 28 days |
| One leap year | 366 | February has 29 days |
| Jan 1 to Dec 31 (same year) | 364 | nights between, not both ends |
| One week | 7 | |
| Four weeks | 28 | not the same as one month |
A year is a leap year if it divides evenly by 4, except century years, which also have to divide evenly by 400. So 2000 was a leap year, 1900 was not, and 2024 was. 2026 is an ordinary 365-day year with a 28-day February. Because the tool works from real calendar dates rather than a fixed 365-day assumption, any leap day sitting inside your range gets counted automatically.
Add/subtract mode exists for deadlines: a 30-day notice period starting January 15 lands on February 14, rolling across whatever month boundary falls in between without you having to count on your fingers. Enter a negative number to move backward instead, useful for working out when something must have started given a fixed deadline. The result always lands on a real calendar date, weekends included; for a count that skips weekends and holidays, the business days calculator is the right tool.
Run March 10, 2026 against July 18, 2026 and the tool reports 130 days. Below that headline number it shows 18 weeks 4 days, which is just 130 split by sevens, and 4.3 months. That last figure deserves a word of explanation, because no calendar has a 30.44-day month: the tool divides by 30.44 because that is the average month length when you spread 365.25 days across 12 months. It is a planning approximation, deliberately labeled as months rather than presented as an exact count. For anything contractual, trust the day count; the month figure is there to give the number scale, not to sign a lease with.
Add mode earns its keep on waiting periods. A 90-day probationary period starting January 15, 2026 runs out on Wednesday, April 15, and the tool crosses the 16 remaining January days, all of February, and all of March without you tracking any of it. Benefits paperwork leans on fixed day counts constantly, 30-day notice windows, 60-day election periods, and the failure mode is always the same: someone counts "three months" on their fingers when the document says 90 days, and lands a day or two off. If the paperwork names a number of days, feed that exact number in here and let the calendar be the calendar.
Enter the dates in either order; the tool takes the absolute difference, so a swapped start and end cannot produce a negative day count or a silent error. That makes it safe for the backward question too: given a deadline, when did the clock most likely start? Subtracting a known day count from a known end date is the same arithmetic run in reverse, and add mode with a negative number does exactly that.
Federal court deadlines run on their own convention, written out in Rule 6(a) of the Federal Rules of Civil Procedure: skip the day the clock starts, count every calendar day after it including weekends and holidays, and if the last day lands on a Saturday, Sunday, or legal holiday, the deadline slides forward to the next day that isn't. A 30-day response window triggered on Thursday, October 1, 2026 technically ends Saturday, October 31, but the filing is due Monday, November 2. This calculator reports the raw arithmetic, October 31, and leaves the rolling to you, because contracts, agency rules, and state courts each keep their own version of the last-day rule, and some have none at all.
Counting backward flips the direction of that safety valve. A rule requiring something "at least 21 days before the hearing" means a weekend landing pushes you earlier, not later, since later would leave you short of the required 21. Take a hearing set for Monday, June 15, 2026: 21 days before is Monday, May 25, which happens to be Memorial Day. The courthouse is closed that day, and Tuesday the 26th would be too late, so the paper is due by Friday, May 22. Whenever a backward count grazes a holiday, resolve it in the cautious direction and read the governing rule's exact wording.
Here is what a set of common notice periods looks like from a single trigger, Thursday, October 1, 2026. Every row came straight out of the add mode above.
| Days added | Lands on | Weekday |
|---|---|---|
| 30 | Oct 31, 2026 | Saturday |
| 60 | Nov 30, 2026 | Monday |
| 90 | Dec 30, 2026 | Wednesday |
| 180 | Mar 30, 2027 | Tuesday |
Only the 30-day window hits a weekend. Whether a Saturday deadline helps or hurts depends entirely on whose obligation it is and what the document says about non-business days, so treat that Saturday as a flag to go read the fine print, not as an answer.
Add 90 days to January 31, 2026 and you land on Friday, May 1. Count "three months" from the same start and most readers, and most statutes, mean April 30, since April has no 31st and month arithmetic clamps to the last day that exists. A full day sits between those two readings, and the gap moves depending on which months the span crosses; a 90-day count that swallows a 28-day February runs ahead of "three months" by up to three days. When a document mixes the two phrasings, the day count wins arguments. It is the only reading with one defensible answer.
"Within 30 days of receipt" hides two questions this calculator cannot settle: what counts as receipt, and whether the receipt day is day zero or day one. The common convention treats the trigger day as day zero, with day one starting the next morning, which matches how this tool counts. But mailed notices often carry their own extension (many state rules add three or five days for service by mail, and federal tax paperwork leans on postmark dates), and "receipt" of an email can mean delivery to a server rather than the morning you read it. Pin down the trigger date first. The arithmetic after that is the easy part, and it is the part this page does.
Add any multiple of 7 days and the weekday stays put: 14, 70, or 364 days from a Tuesday is still a Tuesday. That is why January 1 to December 31 of a common year, 364 nights, begins and ends on the same weekday, and why 2026, which opens on a Thursday, closes on one too. Add 365 instead and you slide one weekday forward; cross a leap day (next up: February 29, 2028) and you slide two. The remainder makes a decent sanity check on any result. Ninety days is 12 weeks and 6 days, so 90 days from a Thursday must be a Wednesday, which is exactly where the October 1 row in the table above landed.
Sources: timeanddate.com date duration reference, U.S. Naval Observatory Astronomical Applications, Federal Rules of Civil Procedure, Rule 6.
Last updated July 18, 2026.
No, and the gap can matter. Thirty days is a fixed count; one calendar month can be 28 to 31 days depending on which month it is. If the text says days, count days with this tool; if it says months, count to the same date number in the later month instead.
This tool counts the nights between the two dates, meaning it counts one endpoint but not both. If your situation requires counting both calendar dates as full days, add one to the result.
Switch to add/subtract mode, enter the deadline as the start date, and enter -90 in the days field. The result is the date 90 days earlier.
Because January 1 to December 31 of the same common year is 364 nights apart, not 365; the 365th day is the start date itself. Counting both endpoints would add the missing day back.
Yes, every calendar day counts equally here. If you need a count that skips Saturdays, Sundays and optionally holidays, use the business days calculator instead.
In federal court, yes: Rule 6(a) rolls a deadline that lands on a weekend or legal holiday to the next working day, and most state courts have a similar rule. A contract only rolls if its own text says so. This tool always reports the raw calendar date and leaves any rolling to the rule that governs your situation.
Usually the day after the trigger: the receipt day is day zero and the next day is day one, which matches how this tool counts. Check the document, though. Service by mail often adds three or five days under state rules, and "receipt" of an email can be defined as server delivery rather than reading.
No. Ninety days from January 31, 2026 is May 1; three months from the same date is April 30, because April has no 31st. Day counts and month counts drift apart by up to three days depending on which months the span crosses.
No, it works in days only, and that is deliberate. "One month from January 31" has no single answer; most conventions clamp it to February 28 in 2026. If your document says months, count to the same date number in the target month by hand and clamp when it does not exist.