Ordinal numeral agreement

To become confident with ordinal numerals, you need to treat them as regular adjectives. They fall into two standard declension paradigms:

• Hard endings: Most ordinals (e.g., nultý [0th], druhý [2nd], čtvrtý [4th], pátý [5th]) take hard endings and decline like hard adjectives (model mladý). Note that nultý (zeroth) is very common in everyday Czech (e.g., nultá lekce).
• Soft endings: The ordinals první (1st), třetí (3rd), and tisící (1000th) take soft endings and decline like soft adjectives (model jarní).

Compound Ordinals (21st, 32nd, etc.)
When dealing with two-word compound ordinals from 21 to 99, like dvacátý první (21st), both parts must decline to match the noun. Alternatively, you can use the interchangeable one-word form (e.g., jedenadvacátý), where only the very end declines. For numbers above 100, the hundreds word can either remain uninflected (e.g., 121st is sto dvacátý první) or be inflected (stý dvacátý první). However, exact hundreds must always decline (e.g., 100th = stý, 200th = dvoustý).

Dates and Years
When expressing "on the [date]", Czech uses the genitive case with no preposition (do not use na or v) because the word den (day) is implied (literally "of the Xth day"). The month must also be in the genitive. For example, "on the 21st of August" becomes dvacátého prvního srpna (or jedenadvacátého srpna). However, prepositions are used for date ranges (e.g., od prvního do pátého = from the 1st to the 5th) or approximations (e.g., kolem dvacátého = around the 20th). In modern everyday speech, years in Czech are often read as cardinal numbers. However, instead of splitting the year into two pairs of tens (like "nineteen ninety-nine"), Czech reads them as hundreds or thousands. For years between 1100 and 1999, the most natural and common way to read them is using the "hundreds" format. For example, 1999 is read as devatenáct set devadesát devět (or tisíc devět set devadesát devět). Note that years can also be read as ordinal numbers, which is formally correct. When doing so, pay attention to the case: the word roku requires the genitive case (e.g., roku tisícího devítistého devadesátého devátého), while v roce requires the locative case (e.g., v roce tisícím devítistém devadesátém devátém). For the year 2000 and beyond, ordinal forms are sometimes used in formal or historical contexts (e.g., v roce dvoutisícím strictly for the year 2000, or v roce dvoutisícím prvním / dva tisíce prvním for 2001). However, it is much more common and safer for learners to use the cardinal form in everyday speech (e.g., v roce dva tisíce, v roce dva tisíce dvacet čtyři).

Monarchs and Popes
When reading the names of historical figures like monarchs or popes, Roman numerals are used and read as ordinal numbers. Crucially, these ordinals must decline to match the case of the noun in the sentence. For example, while the nominative is Karel IV. (read as Karel Čtvrtý), the genitive phrase "statue of Charles IV" is socha Karla IV. and must be read as socha Karla Čtvrtého.

Asking "Which one in order?" (kolikátý)
To ask for an ordinal number, Czech uses the special interrogative word kolikátý (literally "how-many-eth"). It declines exactly like a hard adjective and agrees with the noun it refers to. For example, you can ask Kolikátý jsi skončil? (What place did you finish in?). When asking for the date, you use the genitive form: Kolikátého je dnes? (What is today's date?).

Contrast with Cardinal Numbers
Learners often confuse the rules for ordinals with those for cardinal numbers (one, two, three). While cardinal numbers 5 and higher force the following noun into the genitive plural (e.g., pět dnů = five days), ordinal numbers never do this. They simply agree with the noun's case, regardless of how high the number is (e.g., pátý den = the fifth day).

Orthography Rule
When writing an ordinal as a digit, you must follow it with a period (1., 5., 10.), and crucially, a space must follow the period before the next word (e.g., 1. ledna, never 1.ledna). It is a strict rule in Czech that you cannot attach grammatical suffixes to digits with a hyphen (never write 1-ní or 5-tý). Finally, when writing years as digits, they do not take a period (e.g., v roce 1999, never v roce 1999.), even though they can be read as ordinals.