am, im, um: three words for when

The three preposition contractions cover the vast majority of time expressions. am (= an + dem) is used for days of the week and parts of the day: am Montag, am Morgen, am Abend. im (= in + dem) is used for months, seasons, and centuries: im Januar, im Sommer, im 21. Jahrhundert. um is used for clock time: um 8 Uhr, um halb neun. Memorising these three contractions covers the majority of time expressions a learner will encounter.

Use seit + Dativ + present tense. The tense choice is the top mistake: English speakers use perfect tense ("I have been learning for 3 years"), but German uses the present: Ich lerne seit drei Jahren Deutsch. The action started in the past and is still ongoing — German signals this with present tense + seit, not a perfect construction. seit declines its object in the Dativ: seit einem Jahr, seit drei Monaten, seit dem Montag.

All three can translate as English "for", which is why English speakers confuse them. seit = "since / for up to now" (ongoing; Dativ + present tense): Ich wohne seit zwei Jahren in Berlin. vor = "ago" (completed; Dativ + past tense): Ich bin vor zwei Jahren nach Berlin gezogen. für = "for a bounded, future-oriented duration" (Akkusativ): Ich fahre für eine Woche nach Wien. The temporal reference point determines which to use: still happening now → seit; completed in the past → vor; planned or bounded ahead → für.

A standalone year is stated as a bare cardinal number with no preposition or article: 2026, 1989. If the word Jahr is used, then im Jahr 1989 is correct. The most common English-speaker error is *im 2026 by analogy with im Januar — this is ungrammatical. When stating the year a sentence belongs to, either use the bare number (Er wurde 1990 geboren) or the full phrase im Jahr 1990.

Clock times use um X Uhr for exact hours: um acht Uhr, um 20 Uhr. For half-hours, German counts forward to the next hour: halb neun = half-past eight (8:30), not half-past nine — this is the most common English-speaker confusion. Quarter-hours: Viertel nach acht = quarter past eight (8:15); Viertel vor neun = quarter to nine (8:45). Note: Germans say vor (not zu) for "quarter to" — *Viertel zu neun is non-standard. In spoken German the 12-hour clock is common; in writing the 24-hour clock dominates.

am Montag (capitalized, with article) refers to a specific Monday — this Monday, last Monday, or a contextually anchored Monday: Ich komme am Montag. montags (lowercase, no article, -s suffix) means "on Mondays" in general — every Monday, habitually: Ich gehe montags ins Fitnessstudio. The lowercase -s ending on a day name signals the recurring, habitual reading. This distinction applies to all days: dienstags, mittwochs, donnerstags, freitags, samstags, sonntags.

Time adverbials can appear in Vorfeld (position 1, before the verb, for emphasis) or in the Mittelfeld (the middle field, after the conjugated verb). Within the Mittelfeld the TeKaMoLo rule orders adverbials: Temporal before Kausal before Modal before Lokal. Ich gehe morgen um 10 Uhr langsam nach Hause — morgen um 10 Uhr (Te) comes before langsam (Mo) which comes before nach Hause (Lo). Time adverbials always come first in the middle field.

Both, depending on register. The 24-hour clock is standard in all written and official contexts (timetables, TV schedules, official correspondence): Der Zug fährt um 14:32 ab. In casual spoken conversation Germans typically use the 12-hour clock with context: Wir treffen uns um drei (= 15:00 from context). The digital shorthand uses a colon: 14:32. Spoken times rarely use the word Uhr for quarter-hour forms: you say halb neun and Viertel vor zehn, not halb neun Uhr.