“As of” is a little phrase but I have a lot to say about it. Although it is very common in business writing it can create ambiguity if used incorrectly.
Ambiguity is caused by the fact that “as of” has three different meanings: on, since or from, depending on the context.
Have a look at these sentences:
The contract enters into force as of 1 January 2013. = on
The contract has been effective as of 1 August 2011. = since
The contract is effective as of 1 January 2013. = from
As you see, the meaning of “as of” is determined by the grammar and wording of the sentence in which it is used. So when you use “as of” it is essential that this grammar and wording is correct for the reader to understand what you mean.
The main area of ambiguity is with “as of” meaning “on”. Most native English speakers understand it to mean “on” in the context of “on and after”, as in the first example above, i.e. the contract enters into force on 1 January and remains in force after that date.
But some native English speakers are happy with sentences like this:
The contract was terminated as of 1 January 2012.
To me this is incorrect because a termination cannot happen “on and after” 1 January, but only “on” 1 January. (Some people might dispute this and say that the fact of the contract being terminated continues after 1 January, but to me this is like saying “I drank a cup of tea as of Monday”, and claiming that it’s OK to use “as of” because the fact of the cup of tea being drunk continues after Monday!) But this usage exists nonetheless.
Another area of ambiguity relates to the use of the Present Perfect tense.
Consider this sentence:
The Company purchased 7,000 m3 of wood as of 16 September 2011.
Does this mean the Company purchased (Past Simple) the wood on 16 September 2011, or does it mean the Company has purchased (Present Perfect) the wood since 16 September 2011? The fact that the writer used the Present Simple might lead the reader to think that all the wood was bought on 16 September. But was the writer aware of his choice of tense use?
In my experience, even advanced non-native English speakers make mistakes with the Present Perfect tense. And in the above sentence, this was indeed what had happened – the writer should have written “has purchased”. So if you are not certain that you can use the Present Perfect correctly, do not complicate your writing by using “as of”.
So, after all that, I suggest you follow the advice of professor of linguistics R. L. Trask: “As of – this stiff business expression is best avoided in most writing; use on, since, or from instead, as required.” (Mind the Gaffe: The Penguin Guide to Common Errors in English, Penguin 2002)