> ## Documentation Index
> Fetch the complete documentation index at: https://docs.exponent.finance/llms.txt
> Use this file to discover all available pages before exploring further.

# Yield Token Position

> Onchain YieldTokenPosition account structure and fields

The YieldTokenPosition account tracks a user's deposited YT balance and accrued yield (interest and emissions) for a specific vault. Each user has one yield position per vault, derived as a PDA.

## YieldTokenPosition

```rust theme={null}
pub struct YieldTokenPosition {
    /// Link to address that owns this position
    pub owner: Pubkey,

    /// Link to vault that manages the YT
    pub vault: Pubkey,

    /// Track the YT balance of the user here
    pub yt_balance: u64,

    /// Tracker for interest earned (paid in SY)
    pub interest: YieldTokenTracker,

    /// Tracker for emissions earned (paid in emission tokens)
    pub emissions: Vec<YieldTokenTracker>,
}
```

## YieldTokenTracker

Generic tracker used for both interest and emission yield accrual.

```rust theme={null}
pub struct YieldTokenTracker {
    /// The index is the per-share value of the SY token
    /// Note that the YT balance must be converted to the equivalent SY balance
    pub last_seen_index: Number,

    /// Staged tokens that may be withdrawn
    pub staged: u64,
}
```

## Fields

### YieldTokenPosition

| Field        | Type                     | Description                                              |
| ------------ | ------------------------ | -------------------------------------------------------- |
| `owner`      | `Pubkey`                 | Address that owns this position                          |
| `vault`      | `Pubkey`                 | Vault this position belongs to                           |
| `yt_balance` | `u64`                    | Amount of YT deposited in this position                  |
| `interest`   | `YieldTokenTracker`      | Tracks accrued SY interest                               |
| `emissions`  | `Vec<YieldTokenTracker>` | Tracks accrued emission rewards (one per emission token) |

### YieldTokenTracker

| Field             | Type     | Description                                          |
| ----------------- | -------- | ---------------------------------------------------- |
| `last_seen_index` | `Number` | Last observed per-share index for this tracker       |
| `staged`          | `u64`    | Amount of tokens staged and available for collection |

## How Yield Accrual Works

1. **Deposit YT** — User deposits YT into the position. The `yt_balance` increases and the tracker's `last_seen_index` is set to the vault's current rate.

2. **Stage Yield** — When `stageYtYield` is called, the position calculates earned interest since the last staging:
   * Interest earned = change in exchange rate applied to the YT balance (converted to SY equivalent)
   * Emission rewards = change in emission indexes applied to the total SY balance
   * Earned amounts are added to the `staged` field of each tracker

3. **Collect** — The `staged` amount can be withdrawn via `collectInterest` or `collectEmission`. The `staged` field is decremented by the collected amount.

### Interest Calculation

Interest is computed based on the vault's `final_sy_exchange_rate` (which freezes at maturity). If the current rate exceeds the final rate (post-maturity), earned SY is scaled down proportionally:

```
earned_sy = yt_balance * (1/last_seen_rate - 1/final_rate)
scaled_sy = earned_sy * (final_rate / current_rate)  // if current > final
```