Form 1099-DA closed less of the gap than people assume. Brokers report gross proceeds for transactions from 1 January 2025, but they only report basis for covered securities — digital assets acquired on or after 1 January 2026 and held continuously in that broker's account. Anything bought earlier, or transferred in from self-custody or another platform, is noncovered, and the broker reports no basis at all.

So for most of what a crypto-native business holds today, the taxpayer still has to establish basis themselves. Meanwhile Rev. Proc. 2024-28 ended universal basis pooling and requires allocation wallet by wallet, which is the wrong shape for almost every historical record anyone kept.

This library does that computation.

Install

pnpm add @profullstack/basis-engine

Use

import { prepare } from '@profullstack/basis-engine';

const { form8949, scheduleD, warnings } = prepare(
  [
    { type: 'acquire', id: 'buy-1', at: '2026-01-05', wallet: 'exchange',
      asset: 'ETH', qty: '2', costUsd: '4000' },
    { type: 'transfer', id: 'move-1', at: '2026-03-01', asset: 'ETH',
      from: 'exchange', to: 'cold', qty: '1', feeQty: '0.002', feeUsd: '5' },
    { type: 'dispose', id: 'sell-1', at: '2026-09-01', wallet: 'cold',
      asset: 'ETH', qty: '1', proceedsUsd: '3200' },
  ],
  {
    wallets: [
      { id: 'exchange', kind: 'broker' },
      { id: 'cold', kind: 'self' },
    ],
    method: 'fifo',
    taxYear: 2026,
  },
);

form8949 is grouped into the six boxes with per-box totals; scheduleD carries those totals onto their Schedule D lines. warnings lists everything a human needs to look at before signing.

What it encodes

Wallet-scoped lots. A disposal in one wallet may only consume lots sitting in that wallet, however much of the asset is held elsewhere. This is the rule the library exists to enforce.

Covered-security determination. A lot is covered only when all three hold: it was acquired at a broker wallet, on or after coveredFrom (default 2026-01-01), and it has never been transferred. Moving a lot out of a broker account clears the flag, because no broker knows its basis any more.

Box classification. Term, whether a 1099 is expected, and covered status select the box:

	Basis reported	1099, no basis	No 1099
Short-term	A	B	C
Long-term	D	E	F

Holding period. Long-term requires holding for more than one year: an asset bought 1 January must be sold on 2 January of the following year at the earliest.

Transfers are not dispositions. Moving an asset between your own wallets preserves basis and the original acquisition date. A network fee paid in the transferred asset is a separate disposal, and is treated as one.

Missing basis is surfaced, not invented. Disposing more than a wallet holds produces a zero-basis, short-term lot — the conservative position — flagged with basisUnknown, a quantity-shortfall warning, and UNKNOWN in the date-acquired column. Pass strict: true to throw instead.

Exact arithmetic. Quantities and money are scaled bigints (18 and 6 decimals), never floats. A fully consumed lot hands over every remaining micro-dollar, so splitting lots cannot create or destroy basis. Rows round to cents individually and totals sum the rounded rows, so a printed page always adds up.

Lot selection

fifo (default), lifo, hifo, or spec-id with explicit lotIds. Set it per run via method, or per disposal on the event.

Warnings

Code	Meaning
`quantity-shortfall`	Disposed or transferred more than the wallet holds; basis defaulted to zero.
`unknown-wallet`	A wallet was not declared, so it was treated as self-custody.
`zero-proceeds`	A disposal with no proceeds; confirm it is worthless or gifted.
`negative-basis`	Acquisition cost was negative; basis clamped to zero.

Deliberately not included

Wash sales. Section 1091 applies to stock and securities. Treating digital assets as in scope would change reported gains, so this library does not.
Income recognition. Staking, mining, airdrops and hard forks are ordinary income events. Feed them in as acquire events with the basis you recognised.
Price lookup. Every event carries its own USD figures. Sourcing fair market value is a separate concern with separate evidence requirements.

Development

Requires Node 22.18+ (the test suite runs TypeScript directly via native type stripping). The published package is compiled JavaScript and runs on Node 20+.

pnpm install
pnpm test
pnpm run typecheck
pnpm run build

Not tax advice

This is a computation library. It does not file anything, it is not a substitute for a credentialed preparer, and the positions it takes on unknown basis are conservative defaults you should review.