custom duty

2) Import
Proviso to section 5(1) of IGST Act says that IGST on goods imported into India shall be levied and collected in accordance with the provisions of section 3 of the Customs Tariff Act, 1975 (51 of 1975.) on the value as determined under the said Act at the point when duties of customs are levied on the said goods under section 12 of the Customs Act, 1962. (52 of 1962.)

Export of goods - It can be in two ways - with payment of IGST or without payment of tax under LUT ( ie Zero rated).

Inshort applicable on both import as well as export

Yes IGST is applicable on Asseable Value + Basic Custom Duty
Eg.
Assessable Value 100
BCD @ 10% (10% of 100) 10
Surcharge 10% of BCD 1
_______
Total. 111

IGST @ 18%.(on 111) 19.98