Free Date and Time Tools: Timestamps, Date Gaps, Working Days

Date and time

Three tools for the same underlying question in different clothes: where a date, a duration or a moment actually sits on the calendar — and which of the several plausible answers the situation calls for.

Timestamps

Date differences

Working days

A date is not an instant, and that is where the bugs come from

A calendar date is a label, not a point in time. The moment "3 March" begins depends on which side of the planet you are standing on, so a program that turns a date into a timestamp and back again can easily return 2 March to someone else. That single step is behind most off-by-one-day answers, in spreadsheets as much as in code.

The date difference calculator never takes that step: dates are treated as plain calendar dates and compared directly, so the answer does not depend on the time zone of the machine it runs on. It reports the gap in years, months and days, the total in days and weeks, and the inclusive count as well — because "from the 1st to the 2nd" is a gap of one day and a stay of two, and only you know which one you were asked for.

Timestamps: the unit is a guess, so it gets said out loud

A Unix timestamp is a count of seconds or milliseconds since 1 January 1970, and the digits alone do not tell you which. A ten-digit number is almost always seconds and a thirteen-digit number almost always milliseconds, but "almost always" is doing real work in that sentence: reading one as the other gives a date that is formatted perfectly and is wrong by decades.

So the Unix timestamp converter prints the unit it used, the digit rule behind that decision, and the date the other reading would have produced. It also handles the cases that make people give up and open a search engine: negative values before 1970, values beyond the signed 32-bit range that older systems wrapped into 1901, and the daylight saving hours that either do not exist locally or happen twice. Each of those is named rather than silently resolved.

Working days are a convention, not a fact

Two calendar weeks are fourteen days. Ten working days are also about two weeks, but they end somewhere else entirely, and the gap changes every time a public holiday falls inside it. That difference is the whole reason the business days calculator exists: counting forward from a start date, counting the working days between two dates, and skipping the dates you tell it to skip.

It ships with no holiday calendar, and that is a decision rather than a gap. Public holidays differ by country and region, are set at several levels of government, move every year and are occasionally moved by decree or by a royal funeral. A built-in list would be wrong for most visitors and, worse, confidently wrong about a deadline. Paste your own dates instead, and the tool skips exactly those — including the case where a holiday lands on a weekend that was already being skipped.

Which one do you need?

• How many days, weeks or months between two dates? Use the date difference calculator: the gap in years, months and days, plus totals in days and weeks.
• What date is 20 working days from now, or how many working days are left? Use the business days calculator and paste your own holiday dates so they are skipped.
• A number from a log, and you need the date it stands for? Use the Unix timestamp converter, which states the unit it read and shows UTC, your own zone and any zone you pick.
• When exactly does my notice period end? That is a career question built on the same arithmetic: use the notice period calculator.
• How long is this data encoded as a string? Different question: that is the Base64 encoder and decoder in the encoding and data category.

Other tools and guides on this site

Dates rarely arrive alone; these are the pages that usually come next.

• Career tools — notice periods, offer comparison, equity vesting and the ATS keyword check.
• Notice period calculator — the same date arithmetic applied to the day you resign.
• Job offer comparison calculator — when the date you leave changes what the offer is worth.
• Encoding and data — the other half of the same debugging session: the payload that came with the timestamp.
• All tools — every calculator and utility on the site, grouped by what it is for.

Common questions

Which time zone are the results in?

The timestamp converter prints UTC, your own zone and any zone your browser knows how to name, all at once, and it says which one you are reading. The date difference and business day tools work on plain calendar dates and never convert them through a zone at all — that conversion is the usual cause of an answer that is a day out.

Why does a timestamp have to be told whether it is seconds or milliseconds?

Because the digits alone cannot tell you. 1757000000 read as seconds is September 2025; read as milliseconds it is January 1970. The tool applies the usual ten-digit rule, prints the unit it used, and then prints what the other reading would have been, so a wrong unit is something you can see rather than something you discover a week later.

Why is there no holiday calendar in the business day calculator?

Because a built-in list would be wrong for most visitors. Public holidays differ by country and region, are set at different levels of government, move every year and are sometimes moved by decree. Paste your own dates and the tool skips exactly those — which is also the only version of this calculation you can defend to an employer.

What happens with dates before 1970 or after 2038?

They are handled, and labelled. Negative timestamps are converted normally and flagged as before 1 January 1970, and values outside the signed 32-bit range are shown with the date you would get if something upstream had wrapped them to 32 bits — which is the specific failure that makes older systems report a date in 1901.

Do the date tools give the same answer in every time zone?

They must, and the tests enforce it: the date arithmetic is exercised in very different zones and has to produce identical output in each. Where a calculation genuinely depends on a zone — the daylight saving hour that does not exist, or the one that happens twice — the timestamp converter names the zone it used and describes both sides of the transition instead of silently picking one.