longbill

Receipts for every trade

The house keeps books on you. Now you do too.

Longbill turns your prediction-market history into one honest ledger. See what you’ve actually made, what’s still riding, and how your year could end. It runs on your Mac, read-only.

Follow along

Mac with Apple silicon · macOS 14 or later · 21+

Your year, two ways

What you’ve made. What’s still riding.

Switch between realized P&L and your year with open positions valued at today’s bids. Positions that settle by Dec 31 get their own line, because they decide how your year ends.

  • Realized P&L by month, after fees
  • Every open position: its cost, its value at the bid, and what it pays if it wins or loses
  • A year-end range from the positions still to settle

With open positions at today’s bids · 2026

Realized +$961.10, plus −$16.42 on open positions at today’s bids.

Open at cost$1,135.6510 positions
Value at bid$1,119.23if sold today
Settle by Dec 319of 10 positions

Year-end 2026: realized so far +$961.10. The 9 positions settling by Dec 31 can add −$984.45 to +$1,109.55, so the year ends between −$23.35 and +$2,070.65.

SettlesMarketCostIf it winsIf it loses
Oct 13Northgate Owls vs. Redwood Elk: will the Owls win?Yes × 393$194.16+$198.84−$194.16
Oct 22CPI inflation for September 2026: above 2.5%?Yes × 267$93.45+$173.55−$93.45
Nov 13Fed decision in November 2026: hold rates?Yes × 400$222.12+$177.88−$222.12

7 more open positions, 6 of them settling by Dec 31.

Sample data from a made-up trader, as of Oct 10, 2026.

How it works

Three steps to your real number.

  1. Step 1

    Connect, read-only

    Paste an API key. Longbill keeps it in your Mac’s keychain, and where an exchange offers read-only keys, it refuses anything more. No key? Import the history files your exchange lets you download.

  2. Step 2

    Longbill settles the books

    Every fill, fee, settlement, deposit and withdrawal goes into one ledger. Each closed market is checked against the exchange’s own P&L.

  3. Step 3

    Read your real number

    Realized P&L by month, open positions at today’s bids, and what’s left to settle before Dec 31. After the first pull, refreshes take seconds.

Sportsbooks too

One ledger for every book

Import a sportsbook’s bet history file, or type bets in by hand. They land in the same ledger as your trades.

Tax buckets

Labels you choose

See totals by the labels you pick. Longbill doesn’t choose a tax treatment. You and your accountant do.

Demo

Look around first

A made-up trader’s year comes with the app, so you can try every screen before you connect anything.

Checked against the exchange

Receipts, not vibes.

Every closed market is checked against the exchange’s own P&L. When one doesn’t match, Longbill says which one, by how much, and shows the record behind it.

Snow in Denver on Saturday?

Yes × 120 at 34¢
$40.80
Fees
$1.10
Resolved Yes, paid
$120.00
P&L
+$78.10
Market (sample)LongbillExchange
Snow in Denver on Saturday?+78.10+78.10
Fed cuts in December?−212.40−212.40
Ballon d’Or winner−48.23−48.00$0.23 apart. Longbill shows the fill behind it.

139 of 140 closed markets match. 1 to look at.

What we promise

  • Your trades stay on your Mac. We never see them.
  • Your keys stay in your Mac’s keychain, never on a server.
  • Longbill only reads. It can’t place a trade or move money.
  • Remove an account, and its records go with it.
  • No ads and no tracking, in the app or on this site.

What it isn’t

  • No picks, no locks, no “edge.”
  • No promos, bonuses or referral codes.
  • Not a place to bet. Longbill only keeps the books.
  • Not tax advice. You choose the labels, and your accountant decides what they mean.

Questions

Is it safe to give Longbill an API key?

Your key stays in your Mac’s keychain and never leaves your Mac. Longbill only reads with it, and where an exchange offers read-only keys, Longbill refuses a key that can do more.

Which exchanges does it work with?

US prediction-market exchanges, through read-only API keys or the history files they let you download. We’ll name them here once they’ve agreed to it.

Do I have to connect a key?

No. You can import the history files your exchange lets you download, or type your numbers in.

What about sportsbooks?

Import a sportsbook’s bet history file or type your bets in, and they join the same ledger. Casinos come later.

Can I look around before connecting anything?

Yes. Longbill comes with a demo: a made-up trader’s year, with every screen filled in.

Does it run on Windows or my phone?

Not yet. Longbill runs on Macs with Apple silicon and macOS 14 or later.

What does it cost?

Nothing during the private beta. Pricing isn’t set yet.

Is it tax advice?

No. Longbill totals your numbers by labels you choose. What they mean for your taxes is up to you and your accountant.

Know your real number.

Longbill is in a private beta on Mac. Follow along for the public release.

Follow @longbillapp

Mac with Apple silicon · macOS 14 or later · 21+