What gets removed, and what does not
A business day here is any day that is not a Saturday, not a Sunday, not one of the eleven US federal holidays on its observed date, and not a day you typed into the closed-days box. Saturday can be switched back on, which matters in trades and logistics where a six-day week is normal and the person who quoted you "three business days" was counting one.
The eleven federal holidays are computed from their rules rather than looked up in a table, so every year works and none of them go stale: New Year's Day, Martin Luther King Jr. Day, Washington's Birthday, Memorial Day, Juneteenth, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving and Christmas. Juneteenth only appears from 2021, which is when it was added.
Observed dates move
Federal holidays that land on a weekend are observed on the nearest weekday: Saturday shifts back to the Friday before, Sunday shifts forward to the Monday after. That is what closes offices, so it is what this counts. It has a consequence at the year boundary — when January 1 is a Saturday, the day off lands on December 31 of the previous year, and this tool handles that.
Not everyone follows the federal schedule. Columbus Day and Veterans Day are ordinary working days in a lot of private companies. Many states add their own holidays, and plenty of employers offer floating days instead of fixed ones. Nothing here knows about any of that. Your own calendar, or your counterparty's, is what governs; the closed-days box exists so you can make this match it.
The off-by-one in "N business days"
The single largest source of disagreement is not holidays, it is whether day one is today or tomorrow. "We'll have it to you in three business days" said on a Monday means Thursday if they start counting Tuesday, and Wednesday if they count Monday. Both readings are in common use.
The default here starts the day after, which matches how most shipping and processing windows are quoted — the clock starts when the thing lands on someone's desk, not while it is still in your hand. Switch to counting the start date when the wording is explicit, as in "within 3 business days including today". When the wording says nothing, take the later date and you will be wrong less often.
Filling in your own closed days
Anything not on the federal list goes in the closed-days box, one date per line in MM/DD/YYYY. Shutdown weeks between Christmas and New Year, the Friday after Thanksgiving, plant maintenance days, state holidays, the day your supplier does inventory. If you work somewhere that stays open on federal holidays, do the reverse: switch the federal holidays off and list only the days you actually close. A date you enter that is already a weekend is not removed twice.
The single most useful habit with this tool is to run it against a date you already know the answer to — a delivery that has already arrived, a deadline you have already met — and see whether it agrees. If it does not, the difference will be either the start-date convention or one holiday, and finding out which takes about a minute against the day-by-day list of skipped dates.
Questions people ask
Are state holidays included?
No. Only the eleven federal holidays, on their observed dates. State holidays vary enormously — Patriots' Day closes offices in Massachusetts and Maine and nowhere else, and several states observe days that have no federal equivalent at all. Rather than guess at a location, the tool leaves them out and gives you the closed-days box to add whichever ones apply where you are.
Why does the result differ from the date my supplier quoted?
Almost always one of three things. They count the start date and this does not, or the reverse; they work Saturdays and this does not by default; or they are closed on a day that is not a federal holiday, such as the Friday after Thanksgiving. The day-by-day table of skipped dates in the results makes the third case obvious. For the first two, flip the setting and see whether the dates line up.
Can I count backwards from a deadline?
Yes. Pick the mode that adds business days and enter a negative number. Entering −10 with a deadline as the start date gives you the date ten business days before it, which is the usual way to work out when something has to leave in order to arrive on time. The list of skipped days shows what is in the way.
Does this handle a half-day or an early close?
No, it counts whole days only. A day is either a business day or it is not. Christmas Eve and New Year's Eve are the common cases where an office is technically open but nothing moves after lunch — if that affects the deadline you are counting to, add the day to the closed-days box and treat it as lost.