About
Redmoon Business Date Calculators is a free collection of date and business-day tools — counting working days, projecting deadlines, and applying multi-country holiday rules to the kinds of dates that decide invoices, contracts, filings, and leave. Each calculator focuses on one question and shows exactly how the result was reached.
Why we built it
Date math looks trivial until weekends, public holidays, inclusive-versus-exclusive counting, and country-specific rules collide. A deadline counted by hand is a deadline waiting to be missed. These tools carry the rules so you can rely on a single, defensible date.
How it works
- Runs in your browser. Every calculation happens client-side — your dates never leave the page.
- Multi-country holidays. Pick a country's holiday set, or add your own custom closures.
- Clear breakdowns. See the weekends, holidays, and conventions behind each answer.
- No signup, no cost. The full set of calculators is free to use.
What we mean by a defensible date
Most date disputes are not arithmetic errors. They are disagreements about a convention nobody wrote down. Does a "10-day" notice period mean calendar days or business days? Does the clock start on the day of the triggering event, or the day after? If the deadline lands on a Sunday, does it roll forward — and whose public holidays count? Two people can each count carefully and reach different answers because they silently assumed different rules.
So every calculator is built to make those choices visible rather than bury them. Where a rule is genuinely fixed by statute — the three business days for a Form I-9, the 60 calendar days under the WARN Act — the tool applies it and says so. Where the rule depends on your contract, your jurisdiction, or your payroll calendar, the tool exposes it as an input instead of guessing. And where a calculator cannot know something, its page says that outright: several tools carry a plain statement of what they do not compute, because a limitation you know about is far less expensive than one you discover after the deadline.
How the content is written
Each calculator page carries a hand-written explanation of the rule it implements, a worked example with real dates, and answers to the questions that actually get asked about it. Those are written against the calculator's own logic, not from its title — if the explanation and the code ever disagree, one of them is a bug, and we treat it as one. The blog goes a layer deeper on the rules that have genuine subtlety to them: why "next regular payday" is not a date, why a Schengen 90/180 window is not a calendar quarter, why a 2% early-payment discount is a 37% annualised interest rate.
Where a calculator implements a statutory or regulatory period, its page cites the statute or regulation itself rather than a summary of it, and states the date the rule was last verified. Where it cannot know something — an uncovered state, a tolling rule, a contract term that only you can see — it says so in a section of its own instead of leaving you to find out later. Our methodology page sets out how the holiday data is maintained, how the calculators are tested, and what we got wrong along the way.
Who makes it
It is built by Redmoon Software, which also publishes Redmoon Calculators, Redmoon Converters, and Redmoon Randomizers.
A note on accuracy
The calculators are for information only and are not legal, financial, tax, or professional advice. Holiday data and legal rule sets are simplified — always confirm a real deadline against authoritative sources. See our Terms of Use.