Check out the Withholding Calculator!
You can enter federal estimated tax payments in the Withholding Calculator section near the bottom of the page within Scenario Analysis. Those quarterly estimated payments can be entered where outlined in red below. You can also enter withholding from other sources, as well as amounts applied from the prior year's return.
If you have subscribed to the State Tax Modeling feature, any estimated payments made to the state taxing authority can be entered in the State Withholding section, located just below the federal Withholding section.
NOTE: Because underpayment penalties include a time and interest component in addition to the amount of the payment being made, Holistiplan cannot calculate whether any underpayment penalties apply for a given scenario.
You can also utilize the Field Notes feature to add details to reference later for any amounts listed. If you have any questions at all, please feel free to Contact Support!