(taken from Daily Writing Tips)
Several readers have written to ask which preposition should be used with congratulations. Should we say “congratulations on” or “congratulations for”?
The answer is, “It depends.”
In the singular, congratulation is the action of congratulating. In the plural, congratulations is what one offers to express pleasure in the success or good fortune of another.
The preposition on is used when expressing one’s good wishes in the context of a happy event:
Congratulations on your marriage!
Congratulations on your new baby!
Congratulations on your promotion!
Congratulations on winning the lottery!
Congratulations can be offered as praise for someone’s achievement. In that context, the preposition to use is for:
Congratulations for completing 100 days without an accident!
Congratulations for leading the Scouts to safety!
Congratulations for saving the farm from foreclosure!
Congratulations can also be offered to someone.
The CEO offered congratulations to all her employees.
The townspeople offered congratulations to the utility company for the swift restoration of power.
The word can also be used reflexively: “Go ahead and congratulate yourself. You deserve it.”
Finally, congratulations can be used by itself:
“Everyone shouted ‘Congratulations!’ as the newlyweds descended the staircase.”
Nowadays, wedding guests offer congratulations to both bride and groom, but not so very long ago, it was considered a breach of etiquette to congratulate the bride. The custom was to congratulate the groom and to offer “best wishes” to the bride. The rationale was that the groom deserved to be congratulated because he had won out over his rivals. The bride, on the other hand, received best wishes in the hope that her choice of a husband would prove to have been a wise one.