Concept 2 of 7
12-Hour and 24-Hour: Two Clocks, One Day
Today's big idea
PM hours add 12, AM hours stay, but 12 PM stays 12:00 while 12 AM becomes 00:00.
Both 12 o'clocks are the traps: noon stays 12, midnight drops to 00.
How it works
👀 What's going on?
Your phone may say 7:45 PM while the railway board says 19:45. Both mean the very same moment. One clock restarts at noon and the other never does.
💡 Here's the trick
Look at the chart above. The 12-hour clock runs 1 to 12 twice a day, so it needs AM or PM. The 24-hour clock runs 00:00 to 23:59 once, so it needs no label. Midnight is 00:00 and noon is 12:00.
🪄 How to do it
- 1.Find the row in the chart above that matches your time.
- 2.For a PM time, add 12 to the hour, but leave 12 PM as 12.
- 3.For an AM time, keep the hour, but write 12 AM as 00.
✍️ Try it
Write 7:45 PM on a 24-hour clock. Then: write 12:10 AM on a 24-hour clock.
7:45 PM is after noon, so add 12 to the hour and get 19:45. 12:10 AM is ten minutes after midnight, and midnight is 00:00, so it becomes 00:10.
⚠️ Watch out
You might be thinking 12 PM turns into 24:00 and 12 AM turns into 12:00. Those two are swapped. Noon stays 12:00, and midnight is the one that changes, to 00:00.
🌟 Why this matters
Train tickets, flight boards and bus timetables in India are printed in 24-hour form. Reading one wrongly can cost you a whole day.
Exam tip: Circle AM or PM before you convert, because the two 12 o'clocks behave in opposite ways.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“What is 18:20 in 12-hour format?”
- 1
Check the hour
18 is greater than 12 → it's afternoon. 🕐
- 2
Subtract 12 from the hour
18 − 12 = 6.
- 3
Keep the minutes, add PM
20 minutes stays, label as PM.
- 4
Answer ✓
18:20 = 6:20 PM
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
12 AM = 00 (midnight). 12 PM = 12 (noon). PM after 12 → add 12; 24-hr over 12 → subtract 12.
CLOCK · ROUND 1 OF 3
5:45 PM
Convert to the 24-hour clock
Quick check
✅ VERIFICATION
Written on a 24-hour clock, 12:40 PM is:
⚡ Finish the activity above first to answer.
Keep going!
Up next: Calendar Sense
Div by 4 leaps · div by 100 doesn't · div by 400 leaps again.