Polymarket Units, Rounding and Risk

This page covers the units regular Polymarket (platform: polymarket) uses for prices, sizes, money and time, how the live Bot clamps and rounds order prices onto the market's tick, the market's minimum order size, and how each key in the risk block behaves here. For every key and its allowed values, see All Polymarket parameters.

Units, ticks and rounding

max_position, loop.interval, max_entries_per_market and rules[].size are whole numbers. A fraction is dropped, so 10.9 acts as 10.

Price ticks and rounding

Every Polymarket market has a tick: 0.1, 0.01, 0.001 or 0.0001. Most use 0.01. Every order the Bot sends is a limit order, and before it goes out the live Bot:

1. clamps a buy's price into the allowed band: from the larger of price_floor and one tick, up to the smaller of price_ceiling and 1 minus one tick. A sell is only kept between one tick and 1 minus one tick;
2. rounds it onto the tick: buys round down, sells round up. Rounding never gives you a worse price, as long as price_floor and price_ceiling sit on the tick, but it can make a fill less likely. With a floor between ticks, such as 0.055 on a 0.01 tick, a buy at 0.055 rounds to 0.05, falls below the floor and goes out at 0.06 instead.

The price bounds don't apply to sells, so an exit can always sell at the bid: with the best bid below price_floor, a sell goes out at that bid. A price_ceiling of 1 still stops a buy at 0.99 on a 1-cent tick.

Order size and the market minimum

Polymarket sets a minimum order size per market, usually 5 shares.

• Custom rules check it. A buy whose size ends up below the minimum after the max_position and max_notional clamps is skipped, and the Bot logs an entry_size blocked decision.
• An omitted size on a buy means 1 share. That is below the usual minimum, so the buy is always skipped. Set size to at least the market minimum.
• Built-in strategies raise their orders to the minimum. A panic_fade fade_size, an observation_momentum order or a pre_announcement_drift entry below the minimum is sent at the minimum, and mean_reversion always buys the minimum. An order is never raised past max_position: if the minimum doesn't fit, the entry is skipped with an entry_size blocked decision. See Built-in strategies on Polymarket.
• Fractional sizes are possible. The max_notional clamp divides dollars by price, so the Bot can send an order for, say, 13.33 shares.

Risk keys on Polymarket

risk.max_position

The most shares the Bot may hold in the current market, counting YES and NO together. It counts everything your wallet holds in that market, including shares you bought by hand. How it is enforced depends on the strategy:

If the Bot cannot read your balance, position_size reads 0 and the custom clamp widens rather than blocks. max_notional and max_entries_per_market fail closed instead: if the Bot cannot read your trade history, it skips the buy.

risk.price_floor and risk.price_ceiling

price_ceiling is required and must be above 0 and at most 1. price_floor is optional (default 0) and must be below the ceiling. Both are dollars per share.

Live, they clamp every buy price, as described in Price ticks and rounding. With the floor at 0, the lowest live buy price is one tick. Sells aren't clamped, so a stop-loss below the floor still sells at the bid.

They also gate entries:

• panic_fade, observation_momentum and pre_announcement_drift enter only when the YES price is strictly between the floor and the ceiling. panic_fade also exits, at the bid, if the price drops below the floor.
• mean_reversion buys YES only when the price is above the floor, and buys NO only when the price is below the ceiling.
• spread_capture has no price gate. A floor above the market pushes its bid up, which can cross the book and trade at once unless post_only is true.
• Custom rules are not gated. A custom buy whose midpoint is above the ceiling is sent at the ceiling and may rest.

risk.max_entries_per_market

A hard cap on how many buy orders the Bot places in a market. Set it to 1 for a one-shot strategy. Custom strategies only.

Before each buy, the Bot counts entries already used from the exchange: distinct buy orders in this market's trade history, plus a held position if no buys are recorded yet, plus resting buy orders. If the count has reached the cap, the buy is skipped: Studio reports a max_entries_per_market guardrail and the decision log shows an entry_cap blocked decision. If the exchange history cannot be read, the buy is skipped too.

When this cap is set, it replaces the default guard that skips a custom buy while any order is resting in the market. At 1 the count is exact. Above 1 it is conservative and may stop entries earlier than you expect.

On series_slug and recurring the cap is per market: each new market of the series starts with its full allowance. See Rolling series: what carries over.

risk.max_notional

The total dollars the Bot may commit to buys in the current market. Custom strategies only.

• Spent is the price times size of every buy in this market's trade history, plus the unfilled part of resting buy orders. Fees are not included.
• Sells never free budget. Once spent, it is spent for that market.
• Each buy is cut to the remaining budget divided by the side's midpoint. If the budget is used up, the buy is blocked and Studio reports a max_notional guardrail. If the result is below the market minimum, the buy is skipped. If the history cannot be read, the buy is skipped.
• On series_slug and recurring, the budget resets in every new market. It is not a lifetime spend limit.
• When you save, a buy rule is rejected if size × price_floor is already larger than max_notional.

For example, with max_notional: 10 and a midpoint of 0.50, the first buy is capped at 20 shares. After $4 is spent, the next buy is capped at 12 shares. At $10 spent, buys stop in that market.

Deployment risk limits

Regular Polymarket Bots don't read the deployment risk limits (max contracts per order, max open contracts, daily loss and the rest), so the deploy flow doesn't ask for them. The risk block in your strategy is what limits a Polymarket Bot, so set it as if it were the only limit.