A real Fed book, with its time attached
We requested the contract “Will there be no change in Fed interest rates after the October 2026 meeting?” on 16 October 2026. The YES book was observed at 11:58:31.460 UTC; HowSure completed the response at 11:58:32.334 UTC. These are different clocks. This guide preserves that observation rather than refreshing the example silently.
The best bid was 0.86 and the best ask 0.87, a spread of 0.01 collateral units per share. The captured ask at 0.87 held 152,319.34 shares, so the 500-share estimate consumed one level. Filled shares were 500, unfilled shares 0, and the volume-weighted average price was 0.87. Multiplication gives 500 × 0.87 = 435 gross collateral units.
The verified execution-version and market-fee parameters identified pUSD for this modeled purchase. We retain that unit; the example does not equate pUSD with money in a bank account. The response says filled for a depth calculation, not for an executed trade. No order was submitted.
Gross cost is not the full purchase estimate
For this capture, the model used a fee rate of 0.05 and exponent 1. The covered fee was 500 × 0.05 × 0.87 × (1 − 0.87) = 2.8275 pUSD. Adding it to 435 gives 437.8275 pUSD for the requested 500 shares. These parameters belong to this contract and capture; do not reuse them for every market.
HowSure rounds each consumed level’s modeled fee half-up to five decimals before adding levels. Polymarket documents five-decimal precision without specifying the tie rule. Actual fills and rounding can differ. Funding, withdrawals, conversion, builder surcharges, rebates and intermediary charges are outside this estimate.
A fee amount is only modeled when supported current parameters and exact identity can be checked. If fees are unknown, keep them unknown. Gross cost can still be informative, but it is not a verified all-in total. Book and fee reads also occur separately, so even a successful response is not an atomic quote.
What happens when the first level is too small?
Consider a separate hypothetical book with 200 shares offered at 0.80 and 300 at 0.82. A 500-share buy consumes both: 200 × 0.80 + 300 × 0.82 = 406 gross, or 0.812 per share on average. Multiplying the best ask by 500 would give 400 and miss 6 units of visible-depth cost, before fees.
If the book instead contains only those first 200 shares, report 200 covered, 300 unfilled and 160 gross for the covered part. There is no supported total for all 500. An empty or one-sided book is not evidence that the missing price is zero.
Visible liquidity can disappear before an order reaches a venue. Queue priority, latency, replenishment, routing and subsequent price changes are not simulated. A depth calculation helps compare a requested size with captured liquidity; it cannot guarantee a fill or establish that a trade is worthwhile.
Repeat the calculation through the API
This is one public GET with no key and no paid model. The ID below selects the same October contract; it is not a recommendation. A later call may return another price, unavailable depth or an error. Save the complete response before drawing a comparison.
For your own market, search first and choose the exact returned HowSure ID. Use that same ID for conditions and the book. Do not guess an ID from a title or substitute a whole event URL for one outcome contract. include_cost=true requests the modeled purchase-cost fields.
curl --fail-with-body --show-error --proto '=https' --max-time 30 --get \
'https://www.howsure.com/api/free/v1/contracts/order-book' \
--data-urlencode 'market=polymarket:condition-sha256:cd22800194b2bc38a096e67277f21567ed44b0cd2b746df9d551b2844cc3c781' \
--data-urlencode 'quantity=500' \
--data-urlencode 'outcome=YES' \
--data-urlencode 'side=buy' \
--data-urlencode 'include_cost=true' \
-o howsure-500-yes.jsonRead the result before using the headline number
Check contract identity, the selected book’s status and observed_at, estimate.filled_shares and unfilled_shares, vwap, gross_notional, fee_model.status and purchase_cost. total_for_covered and total_for_requested answer different questions when depth is partial. Preserve the limitations with the numbers when exporting or passing them to an agent.
If a request is invalid, use its field-level error rather than retrying the same input. If it is rate-limited or unavailable, respect Retry-After and retain the old result with its date. Repeated requests do not turn an old quote into an executable one. The same cost reading is available in the contract inspector under Price for your size and in the local MCP tool; neither places orders.
Price and contract interpretation are separate checks. A cheap-looking YES outcome is only meaningful after you know what YES actually requires. Read the exact conditions and their exceptions before comparing prices across outcomes or venues.
Sources & verification
- Retained HowSure calculation, 16 October 2026 at 11:58:32 UTC
- Exact Polymarket October no-change contract
- Polymarket prices and order books
- Polymarket fees
- HowSure HTTP schema and documented model limits
Sources and instructions checked 16 October 2026. Live responses can change. Editorial method and limitations.