komplett
completely
Used as an adverb to express that something is entirely or fully the case; in the sense of 'völlig' (completely) or 'total' (totally).
Ich habe den Termin komplett vergessen.
I completely forgot the appointment.

complete / completely
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completely
Used as an adverb to express that something is entirely or fully the case; in the sense of 'völlig' (completely) or 'total' (totally).
Ich habe den Termin komplett vergessen.
I completely forgot the appointment.

'Komplett' can have two functions. As an adjective before a noun, it is declined and means 'vollständig' (complete). As an adverb intensifying a verb or adjective, it remains unchanged and means 'völlig' (completely).
Er hat eine komplette Modelleisenbahn geschenkt bekommen.
He was given a complete model railway as a gift.
In its function as an adverb ('völlig' (completely), 'total' (totally)), 'komplett' is very common in colloquial speech. It is used to emotionally intensify a statement.
Nach der Wanderung war ich komplett erschöpft.
After the hike, I was completely exhausted.
As an adjective with the meaning 'vollständig' (complete), 'komplett' is often combined with things that consist of several parts. Typical examples are: eine komplette Sammlung (a complete collection), die komplette Ausrüstung (the complete equipment), das komplette Menü (the complete menu).
Für die Reise benötigen Sie eine komplette Winterausrüstung.
For the trip, you need complete winter equipment.
whole / quite
'ganz' and 'komplett' can both express that something is complete. 'ganz' is very common and fits many normal situations, for example 'das ganze Haus' (the whole house) or 'ganz leer' (completely empty). 'komplett' emphasizes more strongly that all parts are there or that really nothing is missing. It often sounds more precise when talking about lists, sets, documents, or plans. Learners confuse the words because both can mean 'complete'. As a memory aid: 'ganz' is more general; 'komplett' fits especially well when you are thinking of all the parts of a whole.

Die Unterlagen für die Reise sind jetzt komplett.
The documents for the trip are now complete.
Vor dem Termin ist Herr Becker die ganze Zeit zu Hause.
Before the appointment, Mr. Becker is at home the whole time.