Most blown accounts are not caused by a bad entry. They are caused by a correct-sized idea placed with an incorrect position size.
The order of decisions
- Decide the maximum you are willing to lose on this trade, as a fixed amount
- Decide where the idea is invalidated — that is your stop distance in pips
- Derive the lot size from those two numbers
- Only then place the order
The arithmetic
Lot size = risk amount / (stop distance in pips x pip value per lot). If you accept 100 of risk, your stop is 25 pips away, and one standard lot moves 10 per pip, then 100 / (25 x 10) = 0.4 lots.
Note the direction of the calculation. The stop distance comes from the chart; the lot size is the output. Choosing a lot size first and then placing a stop wherever it fits is how risk silently becomes unbounded.
Rebates reduce your transaction cost per lot, which improves net results over many trades. They do not reduce the risk of any single position.