[Home](./index.md) > [bitburner](./bitburner.md) > [HacknetServersFormulas](./bitburner.hacknetserversformulas.md) > [coreUpgradeCost](./bitburner.hacknetserversformulas.coreupgradecost.md) ## HacknetServersFormulas.coreUpgradeCost() method Calculate cost of upgrading hacknet server cores. Signature: ```typescript coreUpgradeCost(startingCore: number, extraCores?: number, costMult?: number): number; ``` ## Parameters | Parameter | Type | Description | | --- | --- | --- | | startingCore | number | starting cores | | extraCores | number | amount of cores to purchase (defaults to 1) | | costMult | number | player cost reduction (default to 1) | Returns: number The calculated cost.