Date Calculator
Reckonersweight 1reckoner · computes, doesn't store
How many days until the wedding, how many since the invoice, and what date is ninety days from Tuesday? The Date Calculator does calendar arithmetic so you do not have to count on your knuckles — the span between two dates, or a date plus or minus a stretch of days. It computes the answer and keeps nothing, like a well-mannered oracle.
This is not a screenshot. It's the real tool, running right here — go on, put something in it.
Open the demo full-screen: /demos/date-calculator.html
Questions people ask
How do I calculate the number of days between two dates?
Enter the two dates and it tells you the span. It also works the other way: give it a start date and an offset, and it names the day you will land on.
Is this date calculator private? I am counting down to something personal.
Entirely. It runs offline in your browser inside one HTML file, computes on the spot, and stores nothing — your countdown never leaves the page and there is no account to attach it to.
What would I actually use a date calculator for?
Notice periods, payment terms, visa windows, pregnancy weeks, project deadlines, and settling exactly how overdue the library book is. Any question that starts with how many days.
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