Almost every course teaches the pronunciation of the regular past ending as three lists to memorise: verbs that take one sound, verbs that take another, verbs that gain a whole extra syllable. Three lists is the wrong shape for this problem. There is only one decision, your mouth already knows how to make it, and the reason learners keep getting it wrong is that they are looking at the wrong thing.
The three sounds, and the one question that chooses between them
The past tense ending on regular verbs is pronounced in three different ways in English. Two of them are single consonant sounds that add nothing to the length of the word; the third adds an extra syllable. Which one you pronounce is decided entirely by the final sound of the verb in front of the ending, and by nothing else.
She walked home.
She played tennis.
She waited outside.
Put two fingers on your throat and pronounce the last sound of each verb above, stopping before the ending. On the first line your vocal cords are silent: that final sound is voiceless, sometimes called unvoiced. On the second they are already vibrating, because a vowel sound is always voiced. That vibration, or its absence, is the entire rule. The ending simply continues whatever the sound before it was doing: voiceless before, voiceless ending; voiced before, voiced ending. You are not choosing between two sounds, you are letting the ending copy its neighbour, which is what your mouth wants to do anyway.
After a voiceless consonant
When the verb ends in a voiceless consonant sound, the vocal cords are switched off as you arrive at the ending, and they stay off. There is no vibration to carry over, and no syllable is added.
He stopped the car.
She kissed her mother.
They washed the windows.
We watched the news.
After a voiced consonant, or any vowel
When the verb ends in a voiced consonant sound, or in any vowel sound at all, the vocal cords are already running and simply keep going through the ending. Again no syllable is added, and the word is exactly as long as it was before.
She called her sister.
He opened the door.
They cleaned the kitchen.
We agreed on a price.
Only two sounds add a syllable
Exactly two sounds in the whole language force the extra syllable: the voiceless and voiced pair made by tapping the tongue just behind the top teeth. Those are the two sounds the ending itself is built from, so when a verb already finishes with one of them the ending would be inaudible unless a small vowel came in to separate them. That is all the extra syllable is doing.
The meeting started late.
They decided to wait.
He needed more time.
She counted the votes.
Every one of the four verbs above gains a beat, and every regular verb outside that narrow group keeps exactly the number of syllables it had before. So the extra syllable is the rare case, not the default. If your first language does not allow consonant clusters at the end of a word, you will be tempted to insert that little vowel everywhere, and that single habit is the most audible marker of a learner accent in past tense storytelling, more noticeable in practice than a grammar slip.
An easy way to remember it
Do not memorise which verbs belong to which list. Ask one question instead: is my throat vibrating on the sound immediately before the ending? If the verb already ends in the tapping sound the ending is made of, you get the extra syllable. Otherwise the ending copies its neighbour, voiced for voiced and voiceless for voiceless. One question, asked in the time it takes to say the verb, replaces all three lists.
Spelling will lie to you
Here is the part that catches careful students hardest. The rule is about sound, and only about sound. Learners who reason from the written form look at the last letter, which is not the same as the last sound, and go wrong on exactly the verbs they were being careful about.
He laughed at the idea.
They danced until midnight.
The committee judged the entries.
In the first sentence above, two written letters combine into a single voiceless sound before the ending, so the ending is voiceless. In the second, the letter before the ending is not pronounced the way that letter usually is, and the sound it actually makes is voiceless too. In the third, the letters spell a voiced sound, so the ending is voiced. Not one of the three can be settled by the last letter you see. The silent letter that many verbs carry at the end of their base form is irrelevant for the same reason: it is not a sound, so it decides nothing about what follows it. The reference page on letters that are written but never said is worth a look if those forms are slowing you down.
The same logic, incidentally, governs the plural ending on nouns and the ending that appears on the verb when someone else is acting: copy the voicing of the sound before, and add a syllable only when that sound is too close to the ending to be heard beside it. A wider set of sounds triggers the extra syllable there, so carry the principle across, not the two-sound list.
The exceptions nobody teaches
A small set of words keeps the extra syllable when they work as adjectives, even though the matching verb does not.
He learned the trick in an afternoon.
She is a learned woman.
The priest blessed the crowd.
They sat in blessed silence.
The first and third lines above follow the ordinary rule and gain nothing. In the second and fourth, the identical written word carries an extra beat because it has stopped being a verb and become an adjective. A handful of other adjectives behave the same way and have no everyday verb standing beside them at all.
a wretched night
a crooked line
an aged cheese
the naked eye
Each of the four above is two syllables where you might expect one. The set is closed and somewhat literary in tone, so treat these as vocabulary to be learnt one at a time rather than as a pattern to apply.
How to practise it
Do not sort verbs into lists. Say them aloud, feel the throat, and let the ending follow. Record yourself telling a short story about yesterday and listen back for the little vowel you did not mean to insert; it is far easier to hear in your own recording than in the moment. The lesson that walks through the three endings one at a time gives you the sounds slowly, and the listening set that asks which ending you just heard is the fastest way to prove you can now hear the difference. If the written forms are still slowing you down, the lesson on building the regular past covers the spelling side, and the list of verbs that never take this ending at all saves you from applying the rule where it does not belong. Everything else is sorted on the page that groups lessons by subject.