0 Stamp Duty Calculator (2.0.0)(1 API included) The Stamp Duty calculator API enables you to check the amount of stamp duty payable for the different document types (e.g. Property transfer, lease, share transfer, mortgage, etc.) Note: The calculator API provides only estimates based on the stated assumptions and your inputs. It may not provide for all possible scenarios. By clicking subscribe, you are agreeing to the API Terms and Conditions found below.