Bis, Seit and Seitdem are used very often in sentences, especially in the Nebensatz, but they are used differently, which often leads us to confuse them. Below is a guide to distinguishing these 3 words, with detailed illustrative examples.

1) How to use bis (until)

Usage: bis is understood as the English word "until" and is used to indicate that an action or event ends at some point in time in the future, or at least after the moment you are currently talking about.

Bis is used in the Nebensatz.

Example 1: Sie räumt auf, bis die Kinder aufwachen. (She tidies up until the children wake up.)

The sentence above uses bis to show that the action of the children waking up has not yet happened, so she takes the opportunity to tidy up, which is the action taking place in the present.

Example 2: Ich kann bis 4 Uhr morgens nicht schlafen. (I can't sleep until 4 a.m.)

We understand: before 4 a.m. I do not sleep; by 4 a.m. or after 4 a.m. I have fallen asleep.

2) How to use Seit and Seitdem (since)

Seit and Seitdem are usually used to indicate and mark the point in time at which something began, describing an action that began in the past and continues into the present.

2.1 Seit:

Seit + Dativ

Used with points in time such as days, months, years,…

Example 1: Seit letzter Woche ist ihre Familie umgezogen. (Her family moved away last week)

We understand: Her family moved away, and since then they no longer live there

Example 2: Seit Januar 2022 hat Vinmart seinen Namen in Winmart geändert. (Since January 2022, Vinmart has changed its name to Winmart.)

We understand: Since January 2022 until now, it is no longer called Vinmart but Winmart.

Example 3: Ich war seit 2 Stunden müde. (I have been tired for 2 hours.)

We understand: I have been tired for the past 2 hours and I still feel tired now.

2.2 Seitdem:

Seitdem is a Konjunktion (conjunction)

Seitdem is used in the Nebensatz.

Example 1: Seitdem die Kinder zur Schule gegangen sind, ist es im Haus viel ruhiger geworden. (Since the children started going to school, the house has become much quieter.)

Seitdem is used to mark the point in time from when the children started going to school until the present; while the children have not yet come home from school, the house is still quiet.

Example 2: Ich habe seitdem nichts mehr von ihm gehört. (I haven't heard anything from him since then.)

In the example above there is only one clause, and seitdem comes after the verb; we can see that Seitdem does not have to stand at the beginning of the sentence but depends on each context.