The Spelling Rules for Adding Suffixes:
When to double a letter - and when not to double

Sometimes there is no need to double a letter to protect a short vowel from attack. Look at these examples:

Here, the root word already has two consonants at the end. Even if you add a vowel suffix, the wall is wide enough to protect the short vowel from attack.
This time, the suffix begins with a consonant - so that gives a wall of two consonants, and the short vowel is safe.

Now try these. Be careful! Sometimes you will need to double and
sometimes not.

Add the suffix to the root word	Type the answer
camp + er
bad + ly
sad + ness
flat + est
hid + en
hat + less
fog + y
mug + ful
crack + ed
bump + y
snob + ish
wet + er