Calculation principles
Every exact date result uses real calendar dates rather than average month or year lengths. The web tools run in the browser. Dates entered into a calculator are not sent to LifeDates or stored by the website.
- Exact results use elapsed calendar time.
- Leap days and different month lengths are handled explicitly.
- Pet human-age figures are illustrative comparisons, not biological-age tests.
- Star signs use common Western tropical zodiac date ranges and are presented as cultural birthday facts.
- Medical, legal and official decisions should follow the relevant professional or authority.
Exact age, days lived and birthday calculations
Exact age counts complete years, then complete months, then remaining days. Total days lived is the elapsed whole-day interval between the date of birth and the selected comparison date. Birthday countdowns find the next occurrence of the chosen month and day. The birth year is only needed to calculate the age someone will turn.
For 29 February birthdays, the consumer countdown uses 28 February in a non-leap year and labels that choice in the result. Legal conventions can differ, so official uses should follow the applicable rule.
Round-day milestones add the selected number of elapsed days directly to the starting date. They are not approximated by dividing or multiplying years.
Dog and cat age estimates
The cat comparison uses about 15 human years for the first cat year, 24 by the end of the second year, then four additional human years per cat year. The dog comparison uses the same first two years, then adjusts later years by expected adult size.
These models help people picture life stages. They do not measure health or predict lifespan. The source pages link to AAHA, AAFP, AVMA, Cornell and UC Davis material where relevant, and they state when no veterinarian has reviewed the LifeDates implementation.
Star sign ranges
The star-sign calculator matches month and day to common tropical zodiac ranges. A precise cusp calculation can require birth year, time and place, which this simple calculator does not attempt. Astrology is not presented as a scientific personality assessment.
Published test cases
| Tool | Input | Expected result |
|---|---|---|
| Exact age | 10 March 2000 to 27 August 2026 | 26 years, 5 months and 17 days; 9,666 elapsed days |
| Birthday countdown | 10 March from 27 August 2026 | 195 days to Wednesday, 10 March 2027 |
| Life milestone | 10 March 2000 plus 10,000 days | Tuesday, 27 July 2027 |
| Cat age | 5 years | About 36 human years |
| Dog age | 5-year-old medium dog | About 39 human years |
| Leap-day birthday | 29 February in a non-leap year | 28 February convention, visibly disclosed |
Editorial review and corrections
The LifeDates product team reviews calculator rules, visible explanations, structured data and representative edge cases together. A page is updated when the implementation, explanation or cited source changes. Source-check dates are shown on specialist pet pages.
If a result appears wrong, record the tool, input, expected answer and device date, then email hello@life-dates.com. Do not include another person's private date of birth without their permission.
Check a date for yourself.
Use the free calculators, then keep the birthdays and milestones that matter in LifeDates.
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