How Offerbook calculates its numbers
The sums behind every number on Offerbook: where prices come from, margin after tax, potential profit, gp per hour, ranking and margin held.
Offerbook · Published · 5 min read
Every number on Offerbook can be worked out by hand from other numbers on the same page. This guide lists the sums, so you can check any of them. All values are in gp.
Where prices come from
Prices come from the OSRS Wiki's real-time prices API, which collects trades seen by RuneLite users. Offerbook reads the latest prices every minute, plus 5-minute and 1-hour averages with traded volume. These are real trades, not asking prices, so every price carries the time it last traded. Long-run history on item pages uses the Wiki's daily guide price.
- Instant-buy price (high): the last price someone paid to buy straight away. Flips sell here.
- Instant-sell price (low): the last price someone accepted to sell straight away. Flips buy here.
Margin after tax
Margin is the instant-buy price, minus the instant-sell price, minus the GE tax on selling one at the instant-buy price. The tax is 2% of that price, rounded down, capped at 5,000,000 gp, and zero for exempt items. Here it is on the most traded item right now:
Live data is not available right now. The tool page has the latest.
Potential profit
Potential profit is the margin times the quantity one 4-hour buy-limit window can realistically fill. That quantity is the lowest of three things:
- the item's buy limit;
- 10% of what trades in 4 hours, because one player competing with everyone else rarely gets more than a small slice of the flow;
- what your bankroll can buy at the instant-sell price.
gp per hour is potential profit divided by how long the round trip takes: buying that many and selling them again at that same share of volume, and never faster than the buy limit allows.
How flips are ranked
Rankings start from gp per hour and then scale it down for things that make a flip less likely to work. Each factor is between 0 and 1:
- Price age. The factor halves for every 15 minutes since the older side last traded.
- Fill confidence. Lower when the quantity is a large share of what actually trades.
- Stability. Lower when the mid price has been jumping around.
- Concentration. Lower when one unit costs more than a quarter of your bankroll.
| Item | Buy | Margin | Per 4h |
|---|---|---|---|
| Hallowfell | 2.7m gp | 30,246 gp | 90,738 gp |
| Lightbearer | 4.2m gp | 130k gp | 260k gp |
| Elemental amulet | 1.85m gp | 11,020 gp | 55,100 gp |
| Toxic staff (uncharged) | 8.93m gp | 635k gp | 635k gp |
| Dragon crossbow | 521k gp | 4,323 gp | 82,137 gp |
Margins are after the 2% GE tax. Per 4h is margin times the quantity one buy-limit window can fill, sized to a 10m bankroll.
Reliability
Reliability (some flippers call it margin held) is the share of the last 24 hours' 5-minute windows where the spread was bigger than the tax. It tells you whether a margin is normal for the item or a one-off.
What Offerbook does not do
Offerbook never places offers or touches your account, and the RuneLite plugin only reads your offers to show them to you. Everything is in gp: Offerbook has nothing to do with real-world trading. If a number on the site does not add up from the numbers around it, that is a bug; please email contact@offerbook.gg.
Definitions of every term are in the glossary. The tax calculator and the Screener show these numbers for every item.
Offerbook is gp only and has nothing to do with real-world trading. Prices move, so nothing here is a promise of profit. Every trade is one you make yourself in game.