Grand Exchange tax, profit and break-even prices
A trade plan takes one item, a buy price, a sell price and a quantity, then applies that game's exchange tax. It shows the coins you would spend, the tax, the coins you would receive, the profit or loss, and the lowest whole sale price that covers the buy price. Those figures describe the prices in the plan. The offers still have to fill.
Tax in each game
Both games charge 2% of the sale price and round that tax down to a whole number of coins on each item. A sale under 50 coins is not taxed. Old School caps the tax at 5,000,000 coins on one item. RuneScape has the same 2% and the same 50 coin floor, and it does not use that cap.
Old School can show the last high trade and the last low trade, each with its own time. Those are the last trades recorded for that side. They are not a standing offer, and they do not promise that the next trade fills at that price. RuneScape shows a guide price. That guide price is one planning figure. Putting it on the buy side, the sell side, or both is a choice in the plan.
Some items are exempt. In the current item lists that includes the Old school bond and the Bond. An exempt sale stays untaxed above 50 coins as well.
A Rune scimitar example
Take a Rune scimitar and enter a buy price of 1,000 coins, a sell price of 1,100 coins and a quantity of 10. These prices are assumptions chosen so the rounding is easy to follow. They are not a claim about the latest trade.
The tax on 1,100 coins is 22 coins per item, so 220 coins for ten. The capital is 10,000 coins. The net proceeds are 10,780 coins. The profit is 780 coins, which is a return of 7.80% on the capital. The break-even sale price is 1,020 coins: 1,020 minus 20 coins of tax returns the 1,000 coin buy price, and 1,019 does not.
The same assumptions on a RuneScape Rune scimitar also tax 220 coins, because 22 coins is under the Old School cap. The games diverge on a much larger sale. A sale price of 1,000,000,000 coins is taxed 5,000,000 coins in Old School and 20,000,000 coins in RuneScape. If the buy price is also 1,000,000,000, the Old School break-even sale price is 1,005,000,000 coins.
A sale at 49 coins is untaxed. A sale at 50 coins is taxed 1 coin. A quantity of 0 keeps that per-item tax and break-even price, and the capital, total tax and profit are 0. The return is unavailable, because there is no capital to compare it with. An empty price is also unavailable. It is not treated as zero.
Buy limits
The buy limit is 70 every four hours for the Old School Rune scimitar and 100 every four hours for the RuneScape one. A quantity of 10 sits inside both. The plan does not know how much of that limit is still available. A larger quantity needs more than one four-hour window.
An Old School bond bought and sold at 250,000,000 coins has no tax, so the break-even sale price is 250,000,000 coins. The bond has no alchemy value and no crafting recipe, so the plan links it only to exchange prices. A Twisted bow has an alchemy value and no crafting recipe, so it links to alchemy and not to crafting.
What can still go wrong
The profit is only the gap between the two prices after tax. Someone has to sell to you at the buy price and buy from you at the sell price. A wider gap in the plan can still lose coins if the offers do not fill, or if you change the prices later. An entered price stays put when newer observations arrive. A price that is still following an observation can move when that observation moves. Sharing the plan freezes the figures that were on screen, so the link keeps those assumptions.
Continue from here
Open the Old School plan for this example at Trade profit, or the RuneScape plan at Trade profit. The Rune scimitar has a known alchemy value and can be made at an anvil, so the same quantity continues to exchange prices, alchemy and crafting in Old School, and to exchange prices, alchemy and crafting in RuneScape.
Rule references
The Old School Grand Exchange rules describe per-item tax and exemptions. The RuneScape Grand Exchange rules describe its separate seller tax. The worked prices above are assumptions, not current offers.