gültig
valid
Officially recognized and effective for a certain period of time or under certain conditions.
Dieses Ticket ist nur heute gültig.
This ticket is only valid today.

valid
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valid
Officially recognized and effective for a certain period of time or under certain conditions.
Dieses Ticket ist nur heute gültig.
This ticket is only valid today.

Careful, 'gültig' (valid) is a false friend! It means 'valid' in English, not 'guilty'. The English word 'guilty' is translated into German as 'schuldig'.
Mein Fahrschein ist leider nicht mehr gültig.
Unfortunately, my ticket is no longer valid.
'Gültig' (valid) is the adjective related to the strong verb 'gelten' (to be valid/apply). The sentences 'Das Ticket ist gültig' (The ticket is valid) and 'Das Ticket gilt' (The ticket is valid/applies) have a very similar meaning.
Diese Eintrittskarte gilt für zwei Personen.
This admission ticket is valid for two people.
In connection with official validity, 'gültig' (valid) is often combined with a time expression. Typical patterns are 'gültig bis [Datum]' (valid until [date]) or 'gültig für [Zeitraum]' (valid for [period of time]). It is often used for documents such as tickets, passports, or contracts.
Das Angebot ist nur bis Ende des Monats gültig.
The offer is only valid until the end of the month.
When 'gültig' (valid/applicable) means that something applies or is applicable, it is often followed by the preposition 'für' with the accusative. This limits the scope of validity, for example to a group of people.
Die neue Regelung ist für alle Mitarbeiter gültig.
The new regulation is valid for all employees.
correct / right
'richtig' and 'gültig' can both express that something is correct or can be applied. Use 'richtig' when something is true, error-free, or appropriate, for example an answer or a decision. Use 'gültig' when something is officially valid or effective for a particular situation, for example a ticket, an ID, a rule, or an offer. The words can be confused because both express a kind of 'being right'. The important point is: 'richtig' evaluates the content, while 'gültig' says that something is recognized or allowed.

Am Flughafen ist der Pass noch sechs Monate gültig.
At the airport, the passport is still valid for six months.
Für den Termin im Krankenhaus ist diese Adresse richtig.
This address is correct for the hospital appointment.