interes

/interes/

Cases

SingularPluralWhen to use it
nominativeinteresthe interestintereslethe intereststhe plain dictionary form — the doer of the sentence
genitiveinteresnithe interest'sintereslenithe interests'the owner — whose it is
accusativeinteresnithe interest (as the object)intereslenithe interests (as the object)a specific, known object — whom or what
dativeinteresgeto the interestintereslegeto the interestsdirection or recipient — to where, to whom
locativeinteresdeat / in the interestinteresledeat / in the interestswhere it is; also having — mende bar, "I have it"
ablativeinteresdenfrom the interestinteresledenfrom the interestswhere it comes from; also "than" when comparing
When to use each case
nominative
the plain dictionary form — the doer of the sentence
genitive
the owner — whose it is
accusative
a specific, known object — whom or what
dative
direction or recipient — to where, to whom
locative
where it is; also having — mende bar, "I have it"
ablative
where it comes from; also "than" when comparing

The endings are the same ones the pronouns wear — that page explains when each case is used.

With an owner

One ownedSeveral owned
myinteresimmy interestintereslerimmy interests
yourinteresingyour interestinteresleringyour interests
his / herinteresihis / her interestintereslerihis / her interests
ourinteresibizour interestinteresleribizour interests
you all'sinteresigizyou all's interestintereslerigizyou all's interests
theirinteresleritheir interestinteresleritheir interests

The overlap in the last rows is real, not a mistake: interesleri can mean "his / her interests", "their interest", or "their interests" — context decides.