1. Blocks of time

There are different blocks of time:

a seconda fortnight
a minutea month
an houra year
a daya decade
a weeka century
a weekenda millennium

A time block can also be multiple (more than one):
2 weeks, 3 months, 5 years, etc.

2. When to use ‘every’

The word ‘every’ is used if you repeat the same activity in each time block.

I eat a sandwich every day.He goes to the cinema every month.
My parents call me every week.She visits France every year.
I play football every weekend.The Olympics is every 4 years.
I have a shower every morning.I go to the cinema every 2 weeks.
Sue goes to English class every Monday.Louis cleans the dishes every 3 days.
George and I speak on the phone every 3 months.In France, there is an election every 5 years.
It rains every time I visit Seattle.Saturn completes an orbit of the sun every 29.5 years.

3. The difference between ‘every’ and ‘each’

There is a very small difference between ‘every’ and ‘each’:

every: a series of blocks, considered as a whole
each: individual units, considered individually and uniquely

In other words:
‘Every’ gets used more when all the units get treated exactly the same, with no thought about their uniqueness.
‘Each’ gets used more when each thing is considered and treated separately.

Example sentenceMeaning
Every shopper will receive a discount.There are shoppers, all will get a discount, and no thought is made to think of them individually
I will write to each one of the patients.The patients are considered as individuals, and each will get a note specially written for them
I went to school every Monday.A series of Mondays in a calendar year.
No thought is given to them individually.
I went to school each Monday.One Monday, another Monday, another Monday.
Each Monday is considered as an individual unit.

When talking about time, ‘every’ is more common than ‘each’.

Note: if talking about time units containing multiples (e.g. 2 weeks, 5 years), use every.

I went to the cinema every two weeks.I went to the cinema each two weeks.
He moved house every five years.He moved house each five years.

4. Examples of frequency using ‘every’

I go to the park every Tuesday afternoon.This plant grows half a metre every year.
Rupert reads a story to his daughter every night.After the fire, she had the same nightmare every night for two weeks.
When Lisa lived in Beijing, she ate hot pot every weekend.The shop closes at 3pm every afternoon, except for Friday when it closes at 4.
This teams wins the league every season. It is boring now.I go to the countryside every chance I get.
The company has a team building day every March.Herman goes to the dentist every 6 months.