# Date & time

- Human page: https://happytails.ai/en/date-time-tools/
- Markdown: https://happytails.ai/en/date-time-tools.md
- Structured JSON: https://happytails.ai/agents/en/date-time-tools/index.json
- Visibility: public

## Page guide

Find the tool you need, then open it to get started.

## All date & time

- [Add days](https://happytails.ai/en/date-time-tools/add-days/): Add/subtract calendar days and expose timezone/calendar assumptions. ([Markdown](https://happytails.ai/en/date-time-tools/add-days.md))

- [Age calculator](https://happytails.ai/en/date-time-tools/age-calculator/): Calendar age and next birthday. ([Markdown](https://happytails.ai/en/date-time-tools/age-calculator.md))

- [Business days](https://happytails.ai/en/date-time-tools/business-days/): Custom weekends first. ([Markdown](https://happytails.ai/en/date-time-tools/business-days.md))

- [Date difference](https://happytails.ai/en/date-time-tools/date-difference/): Inclusive/exclusive counting, leap years, calendar dates versus elapsed time. ([Markdown](https://happytails.ai/en/date-time-tools/date-difference.md))

- [Stopwatch](https://happytails.ai/en/date-time-tools/stopwatch/): Measure elapsed time and take lap readings. ([Markdown](https://happytails.ai/en/date-time-tools/stopwatch.md))

- [Time calculator](https://happytails.ai/en/date-time-tools/time-calculator/): Add/subtract hours/minutes/seconds and convert decimal hours. ([Markdown](https://happytails.ai/en/date-time-tools/time-calculator.md))

- [Time card calculator](https://happytails.ai/en/date-time-tools/time-card-calculator/): Daily intervals, breaks and totals. ([Markdown](https://happytails.ai/en/date-time-tools/time-card-calculator.md))

- [Time duration](https://happytails.ai/en/date-time-tools/time-duration/): Start/end times, crossing midnight, breaks, decimal hours and explicit timezone handling. ([Markdown](https://happytails.ai/en/date-time-tools/time-duration.md))

- [Time zone converter](https://happytails.ai/en/date-time-tools/time-zone-converter/): IANA zones, date selection and DST ambiguity. ([Markdown](https://happytails.ai/en/date-time-tools/time-zone-converter.md))

- [Timer](https://happytails.ai/en/date-time-tools/timer/): Set a countdown in seconds. ([Markdown](https://happytails.ai/en/date-time-tools/timer.md))

## Make dates, units and time zones explicit

Date calculations can depend on calendar rules, time zones and whether endpoints are included. A duration in hours is different from a number of calendar days when daylight-saving changes occur.

## How to choose your next step

Choose the intended time zone and verify whether the start or end date counts. For working-day calculations, check which holidays and weekends apply.

## Common questions about date & time

### Are all days exactly 24 hours long?

Elapsed time across a daylight-saving transition can differ from a simple calendar-day count. Use the measure relevant to your schedule.

### Why can the same timestamp show different dates?

A timestamp represents an instant, while a calendar date is interpreted in a time zone. Near midnight, the same instant can fall on different local dates.