# Multiple accounts & chained setups

With several connected accounts you can combine syncs freely — Kalender Sync makes sure no loops or duplicates emerge.

## Typical setups

**Star — one blocks many:**

```text
Personal ──→ Work calendar A
Personal ──→ Work calendar B
```

One sync per target.

**Bundle — several sources block one target:**

```text
Personal ──┐
Club ──────┼──→ Work calendar
Family ────┘
```

A **single** sync with [multiple source calendars](https://docs.kalender-sync.de/en/sharings/multiple-sources/) is enough — all busy times land in the target combined.

**Cross — two calendars block each other:**

```text
Work ⇄ Personal
```

That's a [two-way sync](https://docs.kalender-sync.de/en/sharings/self-sync/) — it counts as **one** sync against your plan limit.

**Chain / hub — everything converges in one calendar:**

```text
iCloud ──→ Outlook ──→ Google
```

Outlook is the "hub" here: it receives from iCloud while feeding Google. Chains like this are explicitly allowed.

## Why this is safe

Kalender Sync marks every blocker it creates and **never syncs it onward**:

- No ping-pong: in the cross setup, an event travels from A to B — but the blocker in B is not mirrored back to A.
- No avalanches: in the chain, the iCloud event creates a blocker in Outlook, but that blocker does **not** flow on to Google. If the event should block Google too, create a direct sync iCloud → Google.
- The only thing **not possible** is one calendar as source *and* target of the same sync (A → A).

## Planning tips

- Sketch first **who should block whom** — one sync per arrow (a double arrow = one two-way sync).
- Blockers are not passed along (see above) — so plan **direct** syncs from every source to every target instead of relying on chain forwarding.
- The number of accounts and syncs depends on your plan → [Plans & limits](https://docs.kalender-sync.de/en/account-billing/plans-limits/).
- Two-way syncs need **exactly two writable** calendars (iCal feeds, for example, are read-only and can't be a target).