Apparently, there is a slight difference, but only in British English: Note: In British English, 'onwards' is an adverb and 'onward' is an adjective. In American English and sometimes in formal British English, 'onward' may also be an adverb. So, depending on where you are, the difference maybe slight.

Understanding the Context

However, they both mean the same thing practically, and most people will understand you if ... Onward sounds odd and is uncommon at the start of a sentence. Here's the definition of onward in the Oxford English Dictionary, adverb, entry 4b. In an uninterrupted advance or succession forward in time.

Key Insights

Cf. on adv. 4a. The definition of on referred to is the same on used in the adverbial phrase "from now on." So the two have some relation to one another. My issue with your example is that ...

Final Thoughts

adverbs - Onward at the beginning of a sentence - English Language ... It's not unheard of for onwards (or usually, onward --see also backward vs. backwards) to be used as an interjection, so there's nothing wrong with using it as a single-word command, like "Go!" It's a bit overwrought, though, so I wouldn't recommend using it in formal settings unless you're being intentionally humorous or colloquial. Can Onwards be used as a sentence? - English Language & Usage Stack ... In Onward, the term screw up is used in place of the word “messed up”, and the phrase is not used as a substitute for strong language, or used in a sexual sense.

1 AS OF would mean "at a certain time onward". AS AT would mean "at a precise time of event". AS FROM would mean "at a certain time onward" just like AS OF, but I still don't quite get it. That leads me to go back and use SINCE.