Add VAT to a price or work backwards from a VAT-inclusive total, in any currency.
Add VAT: VAT = Net × rate, Gross = Net × (1 + rate)
Remove VAT: Net = Gross ÷ (1 + rate), VAT = Gross − Net
Removing 20% VAT from 120 gives 100 net — not 96, which is the common mistake of subtracting 20% of the gross.