What is ISO8601 Date & Time?

ISO8601 is a simple, universal way to write dates and times so there’s no confusion.

🚫 The Problem

• Dates like 01/05/22 can mean different things in different countries.
• This leads to mistakes with meetings, contracts, travel, deliveries — and those mistakes cost time and money.

✅ The ISO 8601 Fix

• Uses a single, globally agreed format: YYYY-MM-DD
  • Example: 2022-09-27 18:00:00.000
• Always written in the same order: year → month → day → hour → minutes → seconds → milliseconds

✅In ISO 8601, durations use letters to show units of time:

P = period (starts the duration)

D = days

T = time section separator

H = hours

M = minutes

S = seconds

🔧 Examples

P3D → 3 days

PT5H → 5 hours

P2DT4H → 2 days and 4 hours

P0DT1H30M → 1 hour 30 mins

🧰 What You Can Use It For

• Dates
• Times of day
• UTC timestamps
• Local times (with timezone offsets)
• Date + time combined
• Time ranges

🤷 Why It Matters

• Removes guesswork
• Reduces errors
• Makes systems talk to each other more reliably
• Works across countries, industries, and software
  
  Related article: How to use ISO8601 Dates & Times in excel