Den and Týden: Irregular Time Nouns

You cannot get through a single Czech conversation without den ("day") and týden ("week"). You say them when you make plans, give dates, count how long something took, and wish someone a good one. The catch is that both are irregular: den in particular loses its vowel the moment you add an ending, turning den into the stem dn-. This page lays out their full declension, the fixed phrases that hide an old genitive, and the one mistake English speakers make every time.

Why den is irregular: the disappearing -e-

Most Czech nouns keep their stem intact when they take case endings. Den does not. The -e- in den is a fleeting vowel (Czech vkladné e) — it exists only to break up the cluster dn when the word stands bare in the nominative singular. Add any ending that begins with a vowel and the prop is no longer needed, so the -e- drops out and you are left with the stem dn-.

So den (one syllable, no ending) becomes dne, dni, dnem — never *dene, *denu, *denem. This is the single most important thing to internalise: the -e- belongs only to the bare nominative (and accusative) singular.

Den — full declension

Den is masculine inanimate. It mixes the regular hrad pattern with some endings borrowed from the soft and -i declensions, which is exactly what makes it irregular. Both forms given in a cell are correct; the first is the more neutral.

Notice that the bare -e- survives only in the nominative and accusative singular (den). Everywhere else the stem is dn-.

The frozen phrase ve dne

One form you will hear constantly is ve dne — "in the daytime, by day". It looks like a locative (dne), and historically it is, but today it works as a fixed adverbial phrase. It usually pairs with v noci ("at night") to contrast day and night.

Do not confuse ve dne (the daytime phrase) with the plain genitive dne used in dates. They are spelled the same but do different jobs.

The genitive dne in dates

Czech dates are built on the genitive. To say "on the fifth of May", you put both the day-number and the month into the genitive, and den itself appears as dne when you write a formal date — dne literally means "of the day".

The leading dne in front of a written date is a hallmark of (formal) register — official letters, contracts, certificates. In everyday speech you simply give the genitive number: pátého května ("the fifth of May"). The mechanics of date genitives are covered on the dates in the genitive page.

dní vs dnů: two genitive plurals

The genitive plural of den has two living forms, and Czech keeps both alive in different niches:

• dnů — the regular, productive genitive plural (like hradů). Use it as your default, especially when a number governs it.
• dní — an older form preserved mainly in time expressions and fixed phrases: před třemi dny uses the instrumental, but pár dní ("a few days"), za pár dní ("in a few days"), and několik dní ("several days") routinely take dní.

Both deset dnů and deset dní ("ten days") are correct and you will hear each. There is no rule that will pick for you — dní simply sounds idiomatic in loose, approximate counts.

To say "how many days ago", Czech uses the instrumental plural dny after před: před třemi dny ("three days ago"). This is the one durational phrase that does not use a genitive, so it is worth memorising as a block.

Týden — the week

Týden ("week") is gentler than den: it keeps its vowel and declines like a regular hard masculine inanimate noun (the hrad pattern), with one wrinkle — the genitive singular is týdne, and the -e- of the second syllable behaves like the fleeting vowel in den. So the stem is týdn-.

Just like den → dn-, the noun týden sheds its second -e- under an ending: týdne, týdnu, týdnem — never *týdenu. The long ý in the first syllable stays put throughout.

Durations: which case after numbers

Both nouns are constantly counted, so the case after a number matters. The rule is the general Czech one: 2, 3, 4 take the nominative/accusative plural (dva dny, tři týdny), while 5 and up take the genitive plural (pět dnů / dní, šest týdnů).

The full logic of the 2–4 versus 5+ split lives on the time and duration in the accusative page, and the broader number system is on the numbers, time and dates page.

Common Mistakes

Key Takeaways

• Den carries a fleeting -e- that survives only in the bare nominative and accusative singular; every other form uses the stem dn- (dne, dni/dnu, dnem; plural dny, dnů/dní, dnům, dnech).
• The genitive plural has two living forms: dnů (default, regular) and dní (idiomatic in loose counts: pár dní, několik dní). "Three days ago" is the instrumental před třemi dny.
• Ve dne ("in the daytime") is a frozen phrase; dne also appears as the genitive in formal dates.
• Týden declines regularly but also drops its second -e- under endings (stem týdn-): týdne, týdnu, týdnem; plural týdny, týdnů.
• The English-speaker trap is keeping the vowel (*denu, *dene, *týdenu). Drop it the moment an ending appears.