What you will find here
Most pages answer one question people search for, such as how many hours lie between two times or when daylight saving time ends. The calculator comes first and the answer updates as you type. Underneath, each page explains the rule that can change the answer, such as whether the end date counts or what happens on the night the clocks change.
The guides take the other route and show the arithmetic step by step. They suit anyone who needs to check a payroll figure or build the calculation into a spreadsheet.
Who writes it
Elizabeth K. Boone writes and builds DateTimeCalcs. She codes the calculators and countdowns, writes each page and guide, and checks the rules behind them against the sources each page lists.
How the pages are made
Each page is plain HTML that can be read before any script runs, so the question, the method and an example answer are always there. The calculator script then runs on your device, in your time zone. The numbers you enter are worked out in your browser and are not sent to DateTimeCalcs, and there are no accounts to create.
Every calculator draws on the same date and time code, and that code has to pass its automated tests before a new version of the site is built. The rules it follows, the test cases and the official sources are set out on the page about how DateTimeCalcs calculates.
When a page is wrong
Send the page address, which already holds the values you entered, and the answer you expected. Confirmed errors are fixed, and the page’s “Last updated” date changes when they are. That date never moves without a real review of the page. The contact page has the address.
Who pays for it
DateTimeCalcs is free, and it shows no ads yet. The plan is to pay for it with display ads in spaces reserved below the calculator, between sections and in the sidebar, where they cannot change a result.
While ads run, the privacy policy lists their cookies and how to opt out.