Why these show their working
Most calculators for this give you a number and nothing else. That is fine when the number is trivia and useless when it is a wage dispute — because the disagreement is almost never about arithmetic. It is about which rule applies.
Whether a fourteen-hour Tuesday is overtime depends on your state. Whether five ten-hour days is ten overtime hours or twenty depends on whether daily and weekly rules are allowed to count the same hours twice — they are not. Whether your employer may round your punch to the quarter hour depends on whether the rounding goes both ways.
So each tool here names the rule it used and cites it. If you disagree with the answer, you can see exactly which assumption to argue with, and take it to someone who can act on it.
What these are not
Not legal advice, and not a substitute for your pay stub. The pay figures are gross — before tax and deductions — and overtime rules apply to non-exempt employees, which not everyone is. Each page says what it does not cover, in plain language, near the answer rather than in small print.
Nothing you type is stored on a server or sent anywhere. The calculations run in your browser; your last settings are kept on your own device so you do not have to enter them twice.