Size for CFDs means number of shares.
Closing price means underlying market price at 10pm (UK time).
If your deal is in GBP
Size × closing price × LIBOR +/- 2.5% ÷ 365
Based on LIBOR one month overnight rate
If your deal is in USD
Size × closing price × US LIBOR +/–2.5% ÷ 360
If your deal is in EUR
Size × closing price × EURIBOR +/–2.5% ÷ 360
The formula uses a 365-day divisor for UK, Singapore and South African shares, and a 360-day divisor for shares in other markets.