Date Calculator
An offline date calculator that runs in your browser: days between, working days, add-a-week, subtract-a-month.
This is not a screenshot. It's the real tool, running right here: go on, put something in it.
Forged into a knife, this tool ages with use: the blades you reach for wear soft, entries you tend keep their bloom, and the years travel with the file through every reforge.
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.
Standing facts
- One HTML file. Opens in any modern browser, on any operating system.
- No account. No login, no sign-up, no e-mail wall.
- No cloud. Nothing leaves your browser: no server, no telemetry, no analytics.
- Yours forever. The file keeps working whether or not Offline.Ltd does.
- Ages with use. Entries you tend keep their bloom; the years travel with the file through every reforge.
In ten years
Date Calculator computes; it doesn't hoard. Open the file in 2036 and it will do the same arithmetic it does today, because the arithmetic is written into the file and nothing about it needs a server to agree.
If Offline.Ltd closes tomorrow, nothing on your machine notices. That isn't a marketing promise; it's simply what a file is.
Getting your data out
There is nothing locked in to get out: copy the numbers, or keep the file. Either way you owe no one a request form. No export queue, no "we'll e-mail you a link within 48 hours", no format that only one vendor can read.
Copy the file to a USB stick, a NAS, a folder your devices already sync. It runs on Windows, macOS, Linux, Android and iOS, online or off, because a browser is the only thing it ever needed.
Who else sees this
Nobody. Date Calculator works out its answer in your browser and forgets it the moment you close the tab: there is no store to breach, because nothing is stored. There is no account, no telemetry, no analytics, and no code in the file that opens a network connection, pull the cable and watch it carry on working. How privacy works across the Reckoners tools →
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.
Go deeper on Date Calculator
More Reckoners
Fits your knife at weight 1. Nothing here is final, Knife follows Life. Reforging within your tier is free, forever. Add it, drop it, reforge it later; the file stays yours either way.