Spilled and SpiltThe verb to spill most commonly means to let a liquid flow over the edge of its container (especially by accident).
To spill is one of those verbs with both an irregular form and a regular form. (See the table below for some others.) The past tense and the past participle can be written as either spilled or spilt. However, they are not fully interchangeable, especially in the US.
Americans Demand SpilledIn America, spilled dominates. The use of spilt as the past tense or past participle of to spill is considered a spelling mistake by many. It will certainly annoy a fair proportion of your readers.
Brits Prefer Spilled but Will Accept SpiltOutside America, spilled is the most common of the two, but spilt is generally accepted. (Spilt used to be more common. The change is almost certainly a result of American influence spreading.)
Verbs with Irregular and Regular FormsThe following verbs (like to spell) can be regular or irregular:
|Verb||Past Simple||Past Participle|
|burn||burned OR burnt||burned OR burnt|
|dream||dreamed OR dreamt||dreamed OR dreamt|
|learn||learned OR learnt||learned OR learnt|
|smell||smelled OR smelt||smelled OR smelt|
|spell||spelled OR spelt||spelled OR spelt|
Usually, the second form (e.g., learnt, dreamt) is more common in British English, but this is not the case with spilt.
The idiom Do not cry over spilt milk is advice not to get upset about something which cannot be changed.
If you're an American, this might be your big chance to use the word spilt. You can always claim you're quoting an old idiom with British origins. (Spilled milk is also frequently written, so please don't think this is a rule. It's more of an opportunity.)