Dates with genitive ordinals

To state when something happens using a full date (day and month), both the day and the month must be in the genitive case. To say 'in [month]', you use v + locative (e.g., v květnu). Note that while most months take the ending -u, červenec and prosinec take -i (v červenci, v prosinci) because they end in the soft consonant -c and follow the soft declension pattern, and září remains unchanged (v září). Other prepositions can also be used with just the month to state when something happens (e.g., do května, během května).

1. The Day
The day is an ordinal number that declines like an adjective. Hard ordinals (like druhý, pátý) take the ending -ého (druhého, pátého). In everyday spoken Common Czech, you will frequently hear this ending pronounced as -ýho (druhýho, pátýho). Soft ordinals (první, třetí) take the ending -ího (prvního, třetího). For compound numbers like 21st or 23rd, both parts take the genitive ending: dvacátého prvního. Alternatively, for numbers in the 20s (21st-29th) and the 31st, you can use the very common single-word inverted format where only the end of the word declines: jednadvacátého, třiadvacátého. Additionally, in everyday spoken Czech, people very frequently replace the tens digit with a cardinal number and only decline the units (e.g., dvacet prvního). However, note that this is strictly non-standard and will be considered incorrect in formal contexts or on Czech language tests. When writing dates with digits, always put a period after the number to show it is an ordinal (e.g., 5. května or 5. 5.). Note that standard Czech typography usually requires a space after the period in dates (e.g., write 5. 5. 2024, not 5.5.2024), but spaces can be omitted when using the two-digit format with leading zeros (e.g., 05.05.2024). Formats without leading zeros must always include spaces. In everyday spoken Czech, when reading the all-numeric format aloud, people often read the month as a nominative ordinal number (e.g., 5. 5. is read as pátého pátý).

2. The Month
The month declines as a noun in the genitive singular. Most months take the ending -a (února), and many of these lose a fleeting 'e' in their stem: leden becomes ledna, březen becomes března, duben becomes dubna, květen becomes května, červen becomes června, srpen becomes srpna, and říjen becomes října. Months ending in the soft consonant -c take the ending -e and also lose their fleeting 'e': červenec becomes července and prosinec becomes prosince. Listopad takes the ending -u (listopadu). Finally, the month září remains unchanged in the genitive (září). Note that while únoru is sometimes used by mistaken analogy, it is considered non-standard in formal Czech.

3. Usage
Use this genitive pattern to answer kdy? (when?) or kolikátého je dnes? (what is the date today?). You do not need any prepositions like 'on' or 'in' because the bare genitive inherently means 'on the [date]'. In formal, written, or business contexts, the genitive date is often introduced by the word dne (e.g., dne 5. května). However, this genitive pattern is frequently used with prepositions like od (from) and do (until) to express timeframes (e.g., od prvního do pátého května). When answering jaké je dnes datum? (what is today's date?), you can use the nominative case (e.g., Dnes je první květen.), but native speakers very frequently and naturally use the genitive case (Dnes je prvního května.). Finally, years are usually read as plain cardinal numbers. Years between 1100 and 1999 are typically read using the 'hundreds' format (e.g., devatenáct set osmdesát devět for 1989). For the 2000s, use thousands (e.g., dva tisíce dvacet pět for 2025). It is also common practice to insert the word roku (in the year) before the year digits (e.g., 5. května roku 2025). Note that in traditional and formal contexts, the year can also be read using genitive ordinal numbers (e.g., roku dva tisíce dvacátého pátého).