er and est and when to use double letters

When using the inflection -er and -est, when do you double the letters? Like big bigger biggest and near nearer and nearest???

The rule given by Swan's "Practical English Usage" is that you double the consonants when a word ends in one vowel + one consonant.

fat - fatter - fattest
thin - thinner - thinnest

BTW: As long as you know the spelling intuitively, you don't have to worry about the rule. (I didn't know the rule before.)

thanks Tom!. I asked everyone and no one I know had the answer!

Beware the words that follow with a vowel and the consonant "w". The above rule doesn't hold good in this case.

low - lower - lowest

Notice the difference in pronunciation between "latter" and "later".

latter ['l@ t..(r)]
later ['lei t..(r)]

"fater" would be pronounced ['fei t..(r)] like "later".
"fatter" is pronounced ['f@ t..(r)] like "latter".

The consonant is doubled because of pronunciation.

Another example: tiger and bigger.

tiger ['tai g..(r)]
bigger ['bi g..(r)]

If you wrote "biger" instead of "bigger",
it would be pronounced ['bai g..(r)] like "tiger".

*If the word consists of one syllable with a consonant+vowel +consonant or
(the last three letters a C+V+C) the last consonant is doubled.
fat fatter sit sitting beg begged
( stop stopped shut shutting)
*If the word has more than one syllable, we double the last consonant only when the stress falls on the last syllable.
begin /bı'gın/ beginning
admit /..d'mıt/ admitting
but enter /'ent..(r)/ entered
answer /'a:ns..(r) answered

**Don't double the last consonant if the word finishes with "w" or "x" ,they are out of this rule.
show showed
draw drawing
***This rule is used for comparatives ,superlatives,forming the regular verbs in past tense and in adding -ing to the verb.

Sorry for the illegible phonetic transcription of "begin and "admit" after sending the message it became like that.