Toward and towards are equally acceptable forms of the word primarily meaning in the direction of. Other than the s at the end, there is no difference between them. Some people differentiate the two words in various ways, but these preferences are not borne out in the usage of most English speakers. Neither form is more formal or informal or more or less logical than the other (the Oxford English Dictionary says towards is more colloquial in British English, but we see no evidence that this is true in 21st-century British writing), so you’re safe using the one that sounds better to you.
But while both these directional words are used in all varieties of English, toward is preferred in American and Canadian English, while towards is preferred in varieties of English from outside North America. These are not rules, however, and exceptions are easily found.
Toward is the older form. It comes from the Old English tóweard, which meant roughly the same as our modern toward.1 Towards is also old, however, as for many centuries the suffixes -ward and -wards have been more or less interchangeable and have given rise to parallel forms of many words—for example, backward and backwards, and forward and forwards.2 Towards became the dominant form in the 17th century and remained ascendant until the Americans took up toward in the 19th century.
This ngram, which graphs the use of toward and towards (as a percentage of all words used) in a large number of British books and periodicals published from 1800 to 2000, shows that the latter has been heavily favored through modern times, though toward might now be gaining ground.
And the next ngram shows the words’ use in American books and periodicals from the same period. It shows that the transition from the now more British towards to the now more North American toward occurred around 1900.
American and Canadian publications prefer toward, as used in these examples:
Scientists are moving toward the conclusion that the eastern cougar was erroneously classified as a separate subspecies in the first place. [NY Times]
To be sure, China is already seeing a shift away from exports toward domestic purchases as its sales to places like Europe falter. [Globe and Mail]
One inning Tuesday went a long way toward erasing any questions the Minnesota Twins might have about their closer. [USA Today]
U.K. and Australian writers heavily favor towards, by a ratio of about 10 to 1. For example, these news organizations use towards much more often than toward:
Libyan rebels advanced west towards Tripoli today after seeing off yet more airstrikes on captured cities by an increasingly desperate Colonel Gaddafi. [Daily Mail]
A few months later, towards December, they circle back completing a round trip of several hundred kilometres. [Guardian]
Scientists are moving towards the conclusion that the eastern cougar was erroneously classified as a separate subspecies in the first place. [Australian Associated Press (article now offline)]
Police began a surveillance operation and on December 23 last year saw David Smith leave his home and head towards a car. [Edinburgh Evening News (article now offline)]