GOAT LabDateLab: 6 offline date, age & Japanese-era (wareki) calculators
DateLab is a free, fully client-side set of 6 date calculators — days between dates with a business-day count, an age calculator, an anniversary countdown, wareki/seireki Japanese-era conversion, an ISO 8601 week-number lookup, and date add/subtract — that run instantly in your browser. All date math is timezone-independent calendar arithmetic.
- Free
- No sign-up
- Works offline
What is DateLab?
DateLab bundles 6 everyday date calculators: a days-between-dates tool that shows total days, whole weeks and Monday–Friday business days at once; an age calculator that reports full years and the days to the next birthday; an anniversary/event countdown; a wareki ⇄ Gregorian converter covering the Meiji, Taisho, Showa, Heisei and Reiwa eras from 1868-10-23 onward; an ISO 8601 week-number lookup; and a date add/subtract tool for adding or subtracting days, weeks or months. Everything is computed locally with no server, no account, and no upload.
How does it work?
Each calculator runs as client-side JavaScript using plain calendar-date arithmetic (UTC epoch-day counting, not local-timezone date parsing), so results never shift depending on the visitor's timezone. Business-day counting excludes Saturdays and Sundays only — public holidays are not built in. Era conversion looks up the exact Gregorian start date of each era (Reiwa began 2019-05-01) and reports the 1-based era year, using the customary '元年' label for year 1 in Japanese.
When should I use it?
Use DateLab to count the days or business days between two project dates, check someone's exact age and next birthday, count down to an anniversary or deadline, convert a Japanese-era date (such as one on a driver's license or koseki record) to the Gregorian calendar and back, look up which ISO week a date falls in for timesheets or planning, or calculate a date a fixed number of days, weeks or months away.
At a glance
| Calculators | 6 (days between, age, countdown, wareki/seireki, ISO week, date add/subtract) |
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| Areas | Day counting, age & events, Japanese-era conversion |
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| Business days | Monday–Friday only — public holidays not excluded |
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| Era coverage | Meiji (1868-10-23) through Reiwa, boundary-accurate |
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| Week numbering | ISO 8601 (Monday-start, Thursday rule) |
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| Processing | 100% client-side — no server, no upload |
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| Account | None — free, no sign-up, works offline |
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| Languages | en, ja, es, zh, de |
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Frequently asked questions
How many business days are between two dates?
DateLab counts Monday–Friday only, excluding Saturday and Sunday; public holidays are not excluded. For example, from Monday 2024-01-01 to Friday 2024-01-05 there are 4 business days (Tue, Wed, Thu, Fri).
What Gregorian date was the start of the Reiwa era?
Reiwa began on 2019-05-01. The day before, 2019-04-30, was the last day of Heisei 31. DateLab's wareki converter covers the Meiji, Taisho, Showa, Heisei and Reiwa eras with exact boundary dates.
How is age calculated?
DateLab compares the current month and day to the birth month and day: the year only increments once the birthday has occurred. For example, someone born 2000-03-01 is still 23 (not 24) on 2024-02-29, the day before their 2024 birthday.
Is my data uploaded?
No. Every calculation runs entirely in your browser. Your inputs never leave your device.
Do I need an account?
No. DateLab is free, needs no sign-up or install, works offline once loaded, and is available in English, Japanese, Spanish, Chinese and German.
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