The Spelling Rules for Adding Suffixes:
When to double a letter.

To understand the doubling rule, it helps to know about vowel and consonant patterns in words.

think back to spelling teaching One way to make a vowel sound long is to put e on the end:
tap, tape bit, bite cod, code tub, tube

In two-syllable words, the first vowel is usually long if there is only one consonant between it and the next vowel:

paper even pilot robot music

The first vowel is short if there are two consonants between it and the
next vowel:

magnet kennel victim bottom butter

Some more examples:


If you are unsure of these vowel and consonant patterns, look at Unit 8.

On page 1 of this unit, you learnt that there are two kinds of suffixes:

English spelling
Vowel suffixes

ing es ed er
en est ish y
able ible al ous
English spelling
English spelling English spelling

English spelling
Consonant suffixes

s less ful ness
ment ly ty
English spelling
English spelling English spelling

If you add a vowel suffix to a short vowel word which has only one consonant at the end, you must double the consonant. If you don't, the vowel sound will change to a long one.

Click on the ear to hear these examples:

  Right Wrong
stop + ed stopped stoped
dig + ing digging diging
fat + er fatter fater

To help you remember this rule, think of the second vowel as an invader. He is trying to attack the first vowel and make it change its ways. If he can get near enough, he will make it say its long sound. Help spelling Rules for Adding Suffixes
Here, there is a strong wall of two consonants. This will protect the short vowel from attack. The invader can't get close, so the first vowel can carry on as before. Help spelling Rules for Adding Suffixes

Now try these. Add the vowel suffix to the root word and type the answer.
Remember, y on the end is a vowel.
The first one has been done for you.

Add the suffix to the root word

Type the answer

swim + ing
shop + ing
hop + ed
flip + er
thin + est
rot + en
grub + y
clap + ing
red + ish
drum + er
mud + y
whip + ed


Skip this exercise and go to the next part of this unit: When NOT to double the consonant. *

* Skip link not available for logged in students.

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Unit 9: Adding suffixes: the spelling rules

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