This is a common question so i was delighted to come across the following in a new fact sheet from Thrombosis UK which I have been given permission to borrow. It has been approved by medical specialist so take it as gospel.
Take the table as soon as you remember and take the following tablet at the usual time and then contiune as normal.
A forgotten does can be taken up to six hours PRIOR to the next dose due. Do not take double a dose to make up for any missed.
Take the tablet as soon as you remember. Do not take more than one tablet in a single day to make up for any forgotten dose.Take the next tablet on the following day and then carry on as normal.
If you are taking either 15mg or 20mg once a day and have forgotten a dose take it as soon as you remember. Do not take more than one tablet in a single day. Take the next tablet on the following day at your usual time and then carry on a normal.
So now you know!