The one rule that keeps small accounts alive
Decide how much you are willing to lose before you decide how much to buy. Risk 1% of a ₱100,000 account and you can be wrong ten times in a row and still have 90% of your capital. Risk 10% and three bad trades cost you a quarter of it. Position size is the bridge between that rule and the buy button.
How the math works
Risk amount = capital × risk %. Risk per share = entry − stop. Shares = risk amount ÷ risk per share, rounded down to the PSE board lot for that price tier. The tool then adds your broker's commission, VAT, PSE and SCCP fees on the way in and the 0.6% stock transaction tax on the way out, so the "real loss" and break-even price are what you would actually see in your ledger.
Board lots matter on the PSE
You cannot buy 37 shares of a ₱12 stock; the lot is 100. For a ₱0.80 stock the lot is 1,000 and for a ₱1,500 stock it is 5. On small accounts the rounding can wipe out your whole position, which is why the tool says so instead of guessing.