voraus
ahead
Expresses a position or movement that is spatially in front of someone or something else.
Die Kinder liefen schnell voraus zum Spielplatz.
The children quickly ran ahead to the playground.

ahead / in advance
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ahead
Expresses a position or movement that is spatially in front of someone or something else.
Die Kinder liefen schnell voraus zum Spielplatz.
The children quickly ran ahead to the playground.

'Voraus' (ahead/in advance) is made up of 'vor' (before/in front of) and 'aus' (out of). It describes the idea of being out in front of a group or position — in other words, being 'up front' or 'ahead'.
Der Läufer war dem Rest des Feldes weit voraus.
The runner was far ahead of the rest of the field.
'Voraus' (ahead/in advance) also functions as a separable prefix for many verbs. Examples are 'vorausgehen' (to go ahead), 'voraussehen' (to foresee), or 'voraussagen' (to predict). The prefix always keeps the meaning of 'beforehand' or 'forward/ahead'.
Niemand konnte diese Entwicklung voraussehen.
No one could foresee this development.
The expression 'im Voraus' (in advance) is a fixed phrase and means 'beforehand' or 'in advance'. It is often used together with verbs like 'bezahlen' (to pay), 'danken' (to thank), or 'planen' (to plan).
Vielen Dank im Voraus für Ihre Hilfe!
Thank you in advance for your help!
The phrase 'jemandem oder seiner Zeit voraus sein' (to be ahead of someone or one's time) means that someone is more progressive, smarter, or more innovative than others. It describes an intellectual or conceptual lead.
Mit ihren Ideen zur Nachhaltigkeit war sie ihrer Zeit um Jahre voraus.
With her ideas about sustainability, she was years ahead of her time.
beforehand
'vorher' and 'im Voraus' both mean that something happens before another point in time. 'vorher' is very general and fits almost all everyday situations: you do something before an appointment, before a meal, or before a trip. 'voraus' by itself often has a spatial meaning, so for the time-related meaning people usually mean 'im Voraus'. Learners may confuse the words because both can mean 'earlier' in terms of time. As a simple rule: for normal time references, 'vorher' is almost always correct; 'im Voraus' sounds especially natural with planning, payment, registration, or thanks.

Bitte bezahlen Sie die Kursgebühr eine Woche im Voraus.
Please pay the course fee one week in advance.
Noah ruft vorher an, damit seine Eltern zu Hause sind.
Noah calls beforehand so that his parents are at home.