Masculine nouns
Feminine nouns
Neuter nouns
Masculine plural
Most masculine nouns ending -el, -en and -er form plural without ending or umlaut
Der Onkel - Die Onkel
Der Haken - Die Haken
Der Computer - die Computer
Some add an umlaut - der Apfel - die Äpfel
If the noun has one syllable and a vowel that can have an umlaut, it frequently adds Umlaut and ‘e’
Der Arzt - Die Ärzte
Der Sohn - Die Söhne
Feminine plural
Most feminine nouns add n/en in the plural
Die Arbeit - Die Arbeiten
Die Frau - Die Frauen
Some have a plural in -e with Umlaut
Die Hand/Die Hände
Two common feminine nouns add umlaut in plural with no ending
Die Mutter/Die Mütter
Die Tochter/Die Töchter
Neuter Plural
Most neuter nouns ending in -el, -en, -er, -chen or -lein form their plural without adding ending or umlaut
Das Messer/Die Messer
Most other nouns add -e in the plural
Das Bein/Die Beine
Some neuter nouns with one syllable form their plural in -er (with umlaut where possible)
Foreign words
Many foreign words and words ending in a full vowel add -s in plural
Das Baby/Die Babys
Das Auto/Die Autos
Many foreign words ending in -us,-a, or -um replace this by -en in plural
Der Rhythmus/Die Rhythmen
Die Firma/Die Firmen