ie

In Latin, ‘ie’ is short for ‘id est’, which means ‘that is’. Use the English term in most cases, particularly in formal texts.
Formal body text
Spell out ‘that is’ in most cases

As with the related Latin abbreviations ‘eg’ and ‘etc’, the use of ‘ie’ in a sentence can look offhand and unprofessional in a formal document.

It is safer to spell out ‘that is’ or use relevant alternatives such as ‘which means’.

The loan is payable fortnightly, which means there are 26 payments each year.
Other contexts
Consider ‘ie’ in less formal communications or where space is limited

In less formal settings, such as internal emails, social media or web communications, ‘ie’ can help to:

We need to receive your application by the end of the month, ie next Wednesday

But even in that context, not everyone will be as familiar with this abbreviation, so it is safer to avoid it.

Punctuation
Place a comma before ‘ie’ but don’t add full stops

If you do use ‘ie’, you don’t need to add full stops to the shortened form (‘i.e.’), but you will usually introduce it with a comma.

You’ll need repay the loan every fortnight, ie 26 times a year.

See also:   eg,  etc,  Latin words