Feature Request: Stamp Duty

ThatBlokeDave

In the UK, a 0.5% stamp duty applies to stock purchases but not sales.

This means for the UK market, I will be looking to create a commission scheme which has a mix of COMM_FIXED and COM_PERC for buying and only a COMM_FIXED when selling.

In other words my broker has a flat fee but I need to take into account the profit killing stamp duty :)

Not sure how many markets this applies to but it would be useful enhancement for the UK.

backtrader

There seems to be some misunderstanding here: COMM_FIXED is not a flat-fee commission, but represents a fixed value per item bought (shares, futures, options, ...)

To put the stamp-duty in place (including a flat-fee) see Docs - User Defined Commissions

You need to override

def _getcommission(self, size, price, pseudoexec):
   '''Calculates the commission of an operation at a given price

   pseudoexec: if True the operation has not yet been executed
   '''

Where size will be > 0 if the operation is a buy and will be < 0 if you are using sell

ThatBlokeDave

@backtrader

Ok - I see... I will take a look. Thanks for the pointer!

backtrader

You would obviously return a fixed amount regardless of size (hence flat) plus the 0.5% stamp duty if size > 0

ThatBlokeDave

I only just got around to looking at this again. If anyone else, has the same requirement, the code I developed is as follows:

class stampDutyCommisionScheme(bt.CommInfoBase):
    '''
    This commission scheme uses a fixed commission and stamp duty for share
    purchases. Share sales are subject only to the fixed commission. 
    
    The scheme is intended for trading UK equities on the main market. 
    '''
    params = (
        ('stamp_duty', 0.005),
        ('commission', 5),
        ('stocklike', True),
        ('commtype', bt.CommInfoBase.COMM_FIXED),
        )

    def _getcommission(self, size, price, pseudoexec):
        '''
        If size is greater than 0, this indicates a long / buying of shares.
        If size is less than 0, it idicates a short / selling of shares.
        '''

        if size > 0:
            return self.p.commission + (size * price * self.p.stamp_duty)
        elif size < 0:
            return self.p.commission
        else:
            return 0 #just in case for some reason the size is 0.

Cheers