процент + Genitive

To express percentages in Russian, you must become comfortable with several grammatical layers:

1. Numeral Government of 'процент'
The case of the word процент is dictated by the last digit of the number in the nominative (except for numbers ending in 11–14):

• Ends in 1 (except 11): один процент (Nominative singular)
• Ends in 2, 3, 4 (except 12, 13, 14): два процента (Genitive singular)
• Ends in 5–9, 0, and 11–14: пять процентов (Genitive plural)
• Fractions and Decimals: With decimal fractions, the fractional part governs the noun, always requiring the genitive singular: 21,5 процента.
• The Numeral полтора (1.5): In the Nominative and Accusative cases, it takes the genitive singular: полтора процента. In oblique cases, the noun switches to the plural: около полутора процентов, с полутора процентами.
• Large Numbers: If the number ends in the words тысяча, миллион, or миллиард, always use the genitive plural: миллион процентов.

2. The Dependent 'Whole'

• Nouns: Use the genitive case directly for most nouns. Example: десять процентов населения (10% of the population). However, for nouns denoting amounts, quantities, or financial concepts (e.g., сумма, зарплата), the preposition от is optional and very common. Example: три процента этой суммы or три процента от этой суммы (3% of this amount).
• Numerals: You must strictly use the preposition от + Genitive. Example: пять процентов от ста (5% of 100).

3. Subject-Verb Agreement
When a percentage phrase is the subject, the verb agreement generally depends on the dependent 'whole' noun:

• Masculine Singular: Used if the numeral ends in 1 (e.g., двадцать один процент проголосовал).
• Plural: Common when the dependent noun is plural, especially for animate or active subjects (e.g., пять процентов студентов сдали экзамен).
• Neuter Singular: Used for quantitative subjects (5 and above) when singular agreement is chosen. The verb is fixed as neuter singular regardless of the dependent noun's gender. Example: пять процентов электората проголосовало (masculine noun, neuter verb) or пять процентов территории было захвачено (feminine noun, neuter verb). It is also used with restrictive particles like всего or только, or as an equally valid alternative to the plural in formal and statistical contexts (e.g., пять процентов студентов сдало).
• Fractions: Mixed numbers and fractions usually take a neuter singular verb (e.g., 21,5 процента проголосовало), though plural is acceptable if there is a plural dependent noun (e.g., 31,5 процента респондентов проголосовали).

4. Oblique Cases
If the whole phrase is in an oblique case (not Nominative or Accusative), both the numeral and the word процент decline and agree in the same case for whole numbers. Crucially, for numbers ending in 2, 3, and 4, the noun процент switches from the singular to the plural in oblique cases (e.g., Nominative: два процента -> Instrumental: с двумя процентами). Example: с пятью процентами (with five percent), около пяти процентов (around five percent). However, fractions always keep the noun процент in the genitive singular regardless of the case (e.g., с двадцатью одной целой и пятью десятыми процента, NOT процентами).

5. Expressing Change
To express an increase or decrease by a certain percentage, use the preposition на followed by the accusative case: Цены выросли на пять процентов (Prices grew by five percent).

6. Compound Adjectives
To describe a noun with a percentage (e.g., a 5% discount), form a compound adjective using the genitive form of the numeral attached to -процентный: пятипроцентная скидка (a five-percent discount), стопроцентная гарантия (a 100-percent guarantee).