
zurückzahlen
to pay back
To return borrowed money to the creditor.
Ich muss meinen Studienkredit in den nächsten zehn Jahren zurückzahlen.
I have to pay back my student loan over the next ten years.
to pay back
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to pay back
To return borrowed money to the creditor.
Ich muss meinen Studienkredit in den nächsten zehn Jahren zurückzahlen.
I have to pay back my student loan over the next ten years.

to pay someone back
To return the favor for a good or bad deed; to respond in the same way.
Für diese Beleidigung werde ich es ihm eines Tages heimlich zurückzahlen.
For this insult, I will secretly pay him back one day.
'Zurückzahlen' (to pay back) is a separable verb. The prefix 'zurück' comes at the end in main clauses. In subordinate clauses or in the infinitive with 'zu', the verb stays together.
Sie zahlt ihm das geliehene Geld nächste Woche zurück.
She is paying him back the borrowed money next week.
The verb is made up of the adverb 'zurück' (back) and the verb 'zahlen' (to pay). The meaning is literal: you return a payment to its origin.
Wann kannst du mir die 50 Euro zurückzahlen?
When can you pay me back the 50 euros?
The person who receives the money or deed back is always in the dative. What is paid back is in the accusative. The structure is: jemandem (dative) etwas (accusative) zurückzahlen.
Ich muss der Bank (Dativ) den Kredit (Akkusativ) zurückzahlen.
I have to pay back the loan (accusative) to the bank (dative).
In the financial meaning, the verb is typically combined with nouns such as 'Schulden' (debts), 'einen Kredit' (a loan), 'ein Darlehen' (a loan), or simply 'Geld' (money).
Er hat all seine Schulden vollständig zurückgezahlt.
He has paid back all his debts in full.
In the figurative meaning, 'zurückzahlen' (to pay back) can express both revenge and gratitude. The phrase 'Das zahle ich dir zurück!' (I'll pay you back for that!) is often a threat.
Für deine Hilfe werde ich es dir eines Tages zurückzahlen.
I will pay you back for your help one day.
to reimburse / report
Both verbs refer to returning money. „Erstatten“ is used mainly when reimbursing specific expenses that have already been paid, while „zurückzahlen“ is used especially for returning borrowed money to the person who provided it. „Erstatten“ fits a bill or expense, while „zurückzahlen“ fits a loan.

Ich muss meiner Schwester das geliehene Geld nächsten Monat zurückzahlen.
I have to pay back the money I borrowed from my sister next month.
Der Arbeitgeber erstattet mir die Kosten für das Zugticket.
My employer reimburses me for the cost of the train ticket.