Я забыл сдачу у кассы, потому что спешил.

I forgot the change at the cash desk because I was in a hurry.

Breakdown of Я забыл сдачу у кассы, потому что спешил.

• я: I
• потому что: because
• у: at
• забыть: to forget
• спешить: to hurry
• сдача: change
• касса: cash desk

Questions & Answers about Я забыл сдачу у кассы, потому что спешил.

Why is забыл used here, not забывал?

Забыл is the perfective past tense: it describes a single completed event—you ended up leaving the change behind.
Забывал is imperfective and usually means a repeated/habitual action (I used to forget...) or focuses on the process (I was forgetting...), which doesn’t fit this one-time situation.

What exactly does сдача mean here? I’ve seen it mean “handing in” too.

Сдача has multiple meanings depending on context. Here it means (cash) change—the money you get back after paying.
It can also mean things like handing in/ сдача экзамена (taking/sitting an exam), but with a shop/cash-register context, сдача = change is the natural interpretation.

Why is сдачу in the accusative case?

Because забыть (to forget/leave behind) takes a direct object in the accusative:
забыл (что?) сдачу = forgot (what?) the change.
Also, сдача is inanimate, so its accusative singular form matches the nominative in shape, but here you can still tell it’s accusative from the verb pattern.

What does у кассы mean literally, and why is кассы in genitive?

У means “by/near/at” (close to something), and it requires the genitive case:
у (кого? чего?) кассы → касса → кассы (genitive singular).
So у кассы is literally “by the cash register / at the checkout”.

Could I say на кассе instead of у кассы?

Sometimes, yes, but it can change the nuance:

• у кассы = by/at the checkout area, near the register
• на кассе = literally on the cash desk/register; in everyday Russian it’s also used to mean at the checkout (especially about paying), but у кассы is often safer for “near the register.”

Why is there a comma before потому что?

Because потому что introduces a subordinate clause of reason (because...). In Russian, the main clause and this subordinate clause are normally separated by a comma:
Я забыл сдачу у кассы, потому что спешил.

Why does the second clause just say спешил without я?

Russian often omits subject pronouns when they’re obvious from context.
спешил is past tense masculine singular, which already matches я (a male speaker) in form. So repeating я would be optional and usually unnecessary.

What if the speaker is female—does спешил change?

Yes. Past tense in Russian agrees in gender:

• male speaker: спешил
• female speaker: спешила
  So a woman would typically say: Я забыла сдачу у кассы, потому что спешила. (Both verbs usually change to match.)

Is спешил the most natural way to say “was in a hurry”? What about торопился?

Both are common:

• спешил = was hurrying / was in a hurry (often sounds a bit more “I was rushing”)
• торопился = was in a hurry (very common, neutral)
  In this sentence, either works well: ...потому что торопился is equally natural.

Does забыть сдачу mean I “forgot about” the change, or I physically left it there?

In this context it strongly implies you physically left it behind (you didn’t take it from the cashier/counter). Russian often uses забыть for “leave behind by mistake,” especially with places: забыл (что-то) у кассы / дома / в машине.

Is the word order fixed? Could I move parts around?

Russian word order is flexible, and changes can shift emphasis. For example:

• Я забыл сдачу у кассы, потому что спешил. (neutral)
• Потому что спешил, я забыл сдачу у кассы. (emphasizes the reason)
• Сдачу я забыл у кассы, потому что спешил. (emphasizes “the change”)

How is у кассы pronounced and stressed?

• у is unstressed, like a short oo sound.
• ка́сса has stress on the first syllable: КА́с-са.
• кассы keeps the same stress: КА́с-сы.