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Year 4 Maths Time

am & pm time

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Theory

am and pm split the day into two halves so we know which time we mean. am runs from midnight to midday (the morning), and pm runs from midday to midnight (the afternoon and evening). This Year 4 page explains the 12-hour cycle, why midday is 12 pm and midnight is 12 am, how to label everyday events like breakfast and dinner, and how to count the hours from a morning time to an afternoon time. Curriculum: VC2M4M03 / AC9M4M03.

A clock face only shows the numbers 1 to 12, so each number comes around twice in one day. We add am or pm to say which one we mean. This is called 12-hour time.

am is for the morning. It runs from midnight up to midday (noon). Waking up, breakfast and the start of school are all am events.

pm is for the afternoon and evening. It runs from midday up to midnight. Lunch in the early afternoon, sport after school, dinner and bedtime are all pm events.

Two special times sit right on the boundary. Midday (noon), in the middle of the day, is written 12 pm. Midnight, at the very start of a new day, is written 12 am.

A day timeline showing the am and pm halves A line from midnight to midnight, 24 hours long. The left half from midnight to midday is the am band, the right half from midday to midnight is the pm band. Breakfast at 8 am, lunch at 1 pm and dinner at 7 pm are marked. 12 am6 am 12 pm6 pm12 am midnightmiddaymidnight am (morning) pm (afternoon / evening) breakfast 8 am lunch 1 pm dinner 7 pm
One whole day: the am half runs midnight to midday, the pm half runs midday to midnight.
A clock showing 9 o'clock, which could be am or pm A clock face with numbers 1 to 12. The long minute hand points to the 12 and the short hour hand points to the 9, so it is 9 o'clock. Because a clock only shows 1 to 12, nine o'clock happens twice a day, so we label it 9 am or 9 pm. 1212 345 678 91011 9 am or 9 pm?
A clock only goes to 12, so 9 o'clock happens twice. am or pm tells the two apart.

am and pm do not need any sums, but these facts are the ones to pin in your memory.

TimeWritten as
Midnight (start of the day)12 am
Morningam
Midday (noon)12 pm
Afternoon and eveningpm
\[ \text{am} : \text{midnight} \rightarrow \text{midday} \]
am : midnight to midday
\[ \text{pm} : \text{midday} \rightarrow \text{midnight} \]
pm : midday to midnight
\[ 12 \text{ hours} + 12 \text{ hours} = 24 \text{ hours} \]
12 hours +12 hours =24 hours
The two to never mix up: midnight is 12 am and midday (noon) is 12 pm. The am half and the pm half are each 12 hours long, so the whole day is 24 hours.

How to decide am or pm

  1. Picture the event. Think about when it happens in the day: waking up, lunch, sport, dinner or bedtime.
  2. Compare it to midday. If it is before midday, in the morning, it is am. If it is after midday, in the afternoon or at night, it is pm.
  3. Write the time and label. Put am or pm after the number, like 8 am or 8 pm. Remember midday is 12 pm and midnight is 12 am.

How to count the hours from am to pm

  1. Count up to midday. Count the hours from the start time to 12 pm.
  2. Count on after midday. Count the hours from 12 pm to the finish time.
  3. Add the two parts. If both times are am (or both pm), just count on from one to the other.

Times with minutes, across midday or midnight

  1. Bridge to 12 o'clock. Count the minutes up to \(12\!:\!00\) (midday or midnight). Past midnight the time changes from pm to am; past midday it changes from am to pm.
  2. Count on the rest. Add whole hours, then the last minutes, and give the answer in minutes or in hours and minutes. Use \(60\) minutes \(= 1\) hour, so \(1\) hour \(10\) minutes is \(70\) minutes.
Example 1 — Morning event
School starts at half past eight in the morning. Write this as a digital time using am or pm.
Solution
\(\text{half past }8\)\(=\)\(8\!:\!30\)
\(\text{morning}\)\(\to\)\(\text{before midday} \to \text{am}\)
8:30 am

School starts at \(8\!:\!30\) am.

Example 2 — Hours through midday
A library opens at 9 am and closes at 3 pm. How many hours is it open?
Solution
\(9\text{ am} \to 12\text{ pm}\)\(=\)\(3\text{ hours}\)
\(12\text{ pm} \to 3\text{ pm}\)\(=\)\(3\text{ hours}\)
\(3 + 3\)\(=\)\(6\text{ hours}\)
3 + 3 = 6 hours

Count to midday, then on from midday. The library is open for 6 hours.

Example 3 — Reading a day timeline
The timeline shows one day. Is the reading lesson at 10 am in the am part or the pm part?
A day timeline with a reading lesson marked at 10 am A line from midnight to midnight. The left half is the am part, the right half is the pm part. A red marker sits at 10 am, inside the am part, before midday. 12 am12 pm12 am midnightmiddaymidnight am part pm part 10 am
Solution
\(10\text{ am}\)\(\to\)\(\text{left of midday}\)
\(\text{left of midday}\)\(\to\)\(\text{am part}\)
10 am is left of midday, so in the am part

The reading lesson is in the am part of the day.

Example 4 — Order the day
Put these three times in order through one day: 5 pm, 8 am, 12 pm.
Solution
\(\text{first}\)\(=\)\(8\text{ am}\)
\(\text{then}\)\(=\)\(12\text{ pm}\)
\(\text{last}\)\(=\)\(5\text{ pm}\)
8 am, 12 pm, 5 pm

am comes before pm, and midday (12 pm) comes before the afternoon, so the order is 8 am, 12 pm, 5 pm.

Example 5 — Across midnight
A train leaves at \(11\!:\!50\) pm and arrives at \(12\!:\!20\) am. How long is the trip?
Solution
\(11\!:\!50\text{ pm} \to 12\!:\!00\text{ am}\)\(=\)\(10\text{ min}\)
\(12\!:\!00\text{ am} \to 12\!:\!20\text{ am}\)\(=\)\(20\text{ min}\)
\(10 + 20\)\(=\)\(30\text{ min}\)
10 + 20 = 30 minutes

Midnight starts the new day, so the time changes from pm to am. The trip takes 30 minutes.

Example 6 — Find the finish time
A film starts at \(2\!:\!35\) pm and runs for \(1\) hour \(50\) minutes. What time does it finish?
Solution
\(2\!:\!35 + 1\text{ h}\)\(=\)\(3\!:\!35\)
\(3\!:\!35 + 25\text{ min}\)\(=\)\(4\!:\!00\)
\(4\!:\!00 + 25\text{ min}\)\(=\)\(4\!:\!25\)
2:35 pm + 1 h 50 min = 4:25 pm

\(50\) minutes is \(25 + 25\). The film finishes at \(4\!:\!25\) pm.

Common pitfalls

Midday is pm, not am. Watch out for 12 o'clock in the middle of the day. It is 12 pm, because it starts the pm half of the day.
Midnight is am. 12 o'clock at night is 12 am, the very start of a new day. Do not write it as 12 pm.
Do not use am and pm together. A time is either am or pm. Write 3 pm, never "3 am pm".
Count through midday. From 11 am to 2 pm is 3 hours: 1 hour up to midday, then 2 more. It is not 9 hours, which is what you get by taking 2 away from 11.

Frequently asked questions

What does am and pm mean?

am is used for times in the morning, from midnight up to midday. pm is used for times in the afternoon and evening, from midday up to midnight. We add am or pm because a clock only shows 1 to 12, so each number comes around twice a day.

Is 12 pm midday or midnight?

12 pm is midday, which is noon in the middle of the day. Midnight, at the very start of a new day, is written 12 am. A lot of people mix these two up.

How do you know if a time is am or pm?

Think about when the event happens. If it is in the morning, before midday, it is am. If it is in the afternoon or at night, after midday, it is pm.

What is the difference between 9 am and 9 pm?

9 am is 9 o'clock in the morning, around the time school starts. 9 pm is 9 o'clock at night, when most children are asleep. The hands are in the same place on a clock, so am and pm tell them apart.

How many hours are in one whole day?

There are 24 hours in one whole day. The hour hand goes around the clock twice in a day: once for the am times and once for the pm times.

Can a time be both am and pm?

No. Every time is either am or pm, never both. You write 3 pm, not 3 am pm.

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