> For the complete documentation index, see [llms.txt](https://docs.kpk.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.kpk.io/funds/infrastructure/onchain-accounting/price-feeds/ankreth.md).
# ankrETH
ankrETH is Ankr's reward-bearing staked-ETH token whose ETH value grows over time. No direct ankrETH/USD Chainlink feed is used; this `ICustomPriceFeed` adapter inverts the token's `ratio()` and applies an ETH/USD price read from the NAV's own primary feed.
{% hint style="info" %}
The ETH/USD term is sourced from the NAV's own selector — see [Base/USD from the NAV's own selector](/funds/infrastructure/onchain-accounting/price-feeds.md#base-usd-from-the-navs-own-selector).
{% endhint %}
**Source:** [`ankrETH_CustomPriceFeed.sol`](https://github.com/karpatkey/onchain-accounting/blob/main/src/prices/protocols/ankrETH_CustomPriceFeed.sol)
***
## Approach
ETH/USD ÷ `ratio()` — `ratio()` is ankrETH-per-ETH, so its inverse is ETH per ankrETH.
ankrETH price feed — how its oracle inputs compose into a USD price, with the staleness gate.
***
## Price calculation
```
price = (ETH/USD) (8) × 1e18 / ratio() (18) // USD, 8 dec
```
| Input | Source | Description |
| ------- | --------------------------------------------------- | ----------------------------------------------- |
| `ratio` | `IankrETH.ratio()` on ankrETH (18 dec) | ankrETH per 1 ETH (decreases as rewards accrue) |
| ETH/USD | NAV base — `getPriceDataNoDivergence(WETH)` (8 dec) | the NAV's primary WETH/USD price, the numerator |
Because `ratio()` is ankrETH-per-ETH, ETH-per-ankrETH = `1e18 / ratio`; the `1e18` numerator cancels the ratio's 18-decimal scale, leaving the ETH/USD feed's 8 decimals. As staking rewards accrue, `ratio()` decreases, so the derived ankrETH price rises. Output decimals are inherited from the ETH/USD feed (8).
***
## Constructor
```solidity
constructor(
address ankrEth_,
address nav_,
address baseAsset_
)
```
| Parameter | Description |
| ------------ | ------------------------------------------------------------------------------------------ |
| `ankrEth_` | ankrETH token address (also the supported underlying) |
| `nav_` | NAVCalculator (proxy) — supplies the base asset's USD price via `getPriceDataNoDivergence` |
| `baseAsset_` | The registered base asset whose USD price is read (WETH) |
***
## Staleness
`getLatestPrice()` returns stale if `ratio()` returns `0`, or if the NAV reports the base asset (WETH) stale — all its feeds stale. The base leg's `updatedAt` comes from the NAV's selected WETH feed. The `ratio()` call has no independent heartbeat.
***
## Chains
Deployed on **Ethereum**.
---
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