Learn Hardcore Japanese: nimotu ga yoteidoori ni todoitara, ansinsuru. - If the package arrives as planned, I will feel relieved.

が marks the grammatical subject of 届く in the subordinate clause: 荷物が届く = “the package arrives.”
は would topicalize: 荷物は予定通りに届いたら、安心する ≈ “As for the package, if it arrives on schedule, I’ll be relieved.” This adds contrast/emphasis on “the package.”
In conditional or relative clauses, が is the neutral choice to mark the subject of that clause. Use は only if you intend a topic/contrast nuance.

What does 予定通りに mean, and why is に there?

予定通り means “as planned / according to schedule.”
The particle に turns it into an adverbial modifier “in the manner of”: “in accordance with the plan.”
You can usually omit に with this kind of adverbial noun: 予定通り届く and 予定通りに届く are both common; に sounds slightly more formal/explicit.
Related expressions:
- 時間通り(に) = on time (by the clock)
- スケジュール通り(に) = according to the schedule

Why is 届いたら in the past form (た) when the meaning is future “if/when it arrives”?

The conditional V-たら uses the past form plus ら but does not necessarily mean past time. It often means “when/if [event] happens (in the future), then…”
Think of it as “once it has arrived, then…”
For a single future event, 届いたら is natural and common: “When it arrives, I’ll be relieved.”

How do ～たら, ～ば, ～と, and ～なら differ here?

届いたら: temporal/conditional, often sequential. Natural for a specific future event. “When it arrives, (then) I’ll be relieved.”
届けば: more hypothetical/conditional, slightly formal/abstract. “If it arrives, I’ll be relieved.”
届くと: general/automatic result or habitual. “Whenever it arrives (on time), I (always) feel relieved.” Less suited to a one-time future event.
届くなら: supposition/assumption based on some premise. “If it’s true that it will arrive on schedule, then I’ll be relieved.”

Could I use 届いてから instead of 届いたら?

Vてから emphasizes a sequence: “after doing X, (then) Y.” It does not express a condition as flexibly as たら.
届いてから安心する = “After it arrives, (then) I’ll be relieved.” This is fine and highlights the order of events.
届いたら安心する can mean “when/if it arrives, I’ll be relieved” and fits both “time” and “condition” readings.

Is 届く the right verb? How is it different from 届ける or 着く?

届く (intransitive): “to be delivered; to reach (the recipient).” Used for mail, packages, notifications. Example: 荷物が届く.
届ける (transitive): “to deliver (something).” Example: 配達員が荷物を届ける.
着く (intransitive): “to arrive (at a place).” Used for people/vehicles/objects arriving at a location. 荷物が倉庫に着いた is possible, but when the sense is “delivered to me,” 届く is the natural choice.

Who is the subject of 安心する? It isn’t stated.

It’s omitted because it’s obvious from context; default is the speaker: “I will be relieved.”
You can make it explicit:
- 私は荷物が予定通りに届いたら、安心する。
- みんなは荷物が予定通りに届いたら、安心する。

How do I make this sentence polite?

Use ます-form: 荷物が予定通りに届いたら、安心します。
You can also add an explicit subject for clarity/politeness: 私は荷物が予定通りに届いたら、安心します。
In customer-facing language, referring to a customer’s package as お荷物 is common: お荷物が予定通りに届いたら、安心します。

Can I say 安心です instead of 安心する? What about 安心になる?

安心する = “to feel relieved” (an action/change of state). Very natural here.
安心です／安心だ describes a state: “(It is) reassuring / (I am) at ease.” With たら, 届いたら安心です can work in contexts like planning: “If it arrives as scheduled, we’re fine.”
安心になる is not the usual way to say “become relieved.” Prefer 安心する or 安心できる (“be able to feel at ease”).
Related nuance: ほっとする = “to feel relieved (with a sense of release),” often used for emotional relief: 届いたらほっとする。

Is it 予定通り or 予定どおり? Which reading is correct?

Pronunciation is よていどおり.
Writing:
- 予定通り (kanji) or 予定どおり (with kana) are both standard.
- Style guides often prefer writing どおり in kana after a noun to make the reading clear (予定どおり).
After verbs/clauses, it’s typically read とおり: 言ったとおり (“as [someone] said”).

Can I drop に after 予定通り? For example: 予定通り届いたら?

Yes. 予定通り届いたら and 予定通りに届いたら are both acceptable. Using に is a bit more explicit/formal; without に is slightly more concise.

Why is there a comma, and are spaces normal in Japanese?

The comma 、 separates clauses; it’s optional but common.
Standard Japanese does not use spaces between words. The spaces you see (荷物　が　予定通り　に…) are for learners’ readability. Normally you’d write: 荷物が予定通りに届いたら、安心する。

How would I say “I’ll be relieved once I confirm it arrived”?

A natural pattern is with 確認:
- 荷物が届いたのを確認したら、安心します。
- 荷物が届いたと確認できたら、安心します。
- 荷物が届いたかどうか確認できたら、安心します。

How do I say the negative idea “If it doesn’t arrive on schedule, I’ll be worried”?

Use the negative conditional:
- 荷物が予定通りに届かなかったら、心配します／心配になる。
心配する (to worry) vs 心配になる (to become worried) are both fine; になる emphasizes the change of state.

Why is 安心する in nonpast (する) instead of past (した)?

Nonpast covers both present habitual and future. Here it means a future result: “I will be relieved.”
For a past event, use past: 荷物が予定通りに届いたら、安心した。 = “When it arrived on schedule, I felt relieved.”

Can I change the word order, like 予定通りに荷物が届いたら?

Yes. Adverbials like 予定通りに can move around:
- 荷物が予定通りに届いたら、安心する。
- 予定通りに荷物が届いたら、安心する。
Both are natural; choose what flows best in context.

Could I use 時 instead of たら? What’s the nuance?

届いた時(に) = “when it arrives.” It’s a neutral time expression.
届いたら often implies a sequence/condition leading to the next action; it’s very natural for “Once it arrives, (then) …”
In many cases they overlap:
- 荷物が届いた時に安心する ≈ 荷物が届いたら安心する. たら can feel a bit more event-driven/sequential.