Cost Basis Engine

Cost Basis Engine

Compute cost basis for crypto trades using multiple accounting methods and compare the resulting tax liability across methods. This skill handles the full complexity of on-chain activity: partial sells, token migrations, airdrops, staking rewards, LP entry/exit, and multi-hop swaps.

Disclaimer: This skill provides computational tools for informational purposes only. It does not constitute tax, legal, or financial advice. Consult a qualified tax professional for your specific situation. Tax law varies by jurisdiction and changes frequently.

Prerequisites

• Python 3.10+
• No external dependencies required (standard library only)
• Trade history as a list of dicts or CSV with columns: date, action, token, quantity, price_usd, fee_usd

Methods Overview

1. FIFO (First-In, First-Out)

Sell the oldest lots first. This is the default method in the US if no other method is elected.

def fifo_sell(lots: list[dict], sell_qty: float, sell_price: float) -> list[dict]:
    """Sell using FIFO. lots sorted oldest-first."""
    remaining = sell_qty
    realized = []
    while remaining > 0 and lots:
        lot = lots[0]
        used = min(lot["qty"], remaining)
        gain = (sell_price - lot["cost_per_unit"]) * used
        realized.append({"qty": used, "basis": lot["cost_per_unit"], "gain": gain})
        lot["qty"] -= used
        remaining -= used
        if lot["qty"] <= 0:
            lots.pop(0)
    return realized

Partial sell example

You hold three lots of TOKEN:

• Lot A: 100 units @ $1.00 (oldest)
• Lot B: 50 units @ $2.00
• Lot C: 75 units @ $1.50

You sell 120 units at $3.00:

• 100 from Lot A: gain = (3.00 - 1.00) * 100 = $200
• 20 from Lot B: gain = (3.00 - 2.00) * 20 = $20
• Total realized gain: $220
• Lot B remainder: 30 units @ $2.00

2. LIFO (Last-In, First-Out)

Sell the newest lots first. Reverses the order compared to FIFO.

def lifo_sell(lots: list[dict], sell_qty: float, sell_price: float) -> list[dict]:
    """Sell using LIFO. Pops from end (newest first)."""
    remaining = sell_qty
    realized = []
    while remaining > 0 and lots:
        lot = lots[-1]
        used = min(lot["qty"], remaining)
        gain = (sell_price - lot["cost_per_unit"]) * used
        realized.append({"qty": used, "basis": lot["cost_per_unit"], "gain": gain})
        lot["qty"] -= used
        remaining -= used
        if lot["qty"] <= 0:
            lots.pop()
    return realized

Using the same lots and selling 120 at $3.00 with LIFO:

• 75 from Lot C: gain = (3.00 - 1.50) * 75 = $112.50
• 45 from Lot B: gain = (3.00 - 2.00) * 45 = $45
• Total realized gain: $157.50

3. HIFO (Highest-In, First-Out)

Sell the highest-cost lots first to minimize realized gains.

def hifo_sell(lots: list[dict], sell_qty: float, sell_price: float) -> list[dict]:
    """Sell using HIFO. Sort by cost descending, consume highest first."""
    lots.sort(key=lambda x: x["cost_per_unit"], reverse=True)
    remaining = sell_qty
    realized = []
    for lot in lots:
        if remaining <= 0:
            break
        used = min(lot["qty"], remaining)
        gain = (sell_price - lot["cost_per_unit"]) * used
        realized.append({"qty": used, "basis": lot["cost_per_unit"], "gain": gain})
        lot["qty"] -= used
        remaining -= used
    lots[:] = [l for l in lots if l["qty"] > 0]
    return realized

Same lots, selling 120 at $3.00 with HIFO:

• 50 from Lot B ($2.00, highest): gain = (3.00 - 2.00) * 50 = $50
• 70 from Lot C ($1.50, next highest): gain = (3.00 - 1.50) * 70 = $105
• Total realized gain: $155
• Remaining: Lot A 100 @ $1.00, Lot C 5 @ $1.50

4. Specific Identification

The trader explicitly selects which lots to sell. Provides maximum control but requires meticulous record-keeping. Each lot must be uniquely identifiable (e.g., by purchase date and time, or a lot ID).

def specific_id_sell(lots: dict[str, dict], lot_ids: list[tuple[str, float]],
                     sell_price: float) -> list[dict]:
    """Sell specific lots by ID. lot_ids = [(lot_id, qty_to_sell), ...]"""
    realized = []
    for lot_id, sell_qty in lot_ids:
        lot = lots[lot_id]
        used = min(lot["qty"], sell_qty)
        gain = (sell_price - lot["cost_per_unit"]) * used
        realized.append({"lot_id": lot_id, "qty": used, "basis": lot["cost_per_unit"], "gain": gain})
        lot["qty"] -= used
        if lot["qty"] <= 0:
            del lots[lot_id]
    return realized

5. Proportional / Average Cost Method

Compute a single weighted-average cost per unit across all held lots. Every sell uses that average cost. The average updates after each buy.

def average_cost_basis(lots: list[dict]) -> float:
    """Compute weighted average cost per unit across all lots."""
    total_cost = sum(l["qty"] * l["cost_per_unit"] for l in lots)
    total_qty = sum(l["qty"] for l in lots)
    if total_qty == 0:
        return 0.0
    return total_cost / total_qty

def average_cost_sell(lots: list[dict], sell_qty: float, sell_price: float) -> dict:
    """Sell using average cost. Reduces all lots proportionally."""
    avg = average_cost_basis(lots)
    total_qty = sum(l["qty"] for l in lots)
    sell_qty = min(sell_qty, total_qty)
    gain = (sell_price - avg) * sell_qty
    # Reduce each lot proportionally
    ratio = sell_qty / total_qty
    for lot in lots:
        lot["qty"] *= (1 - ratio)
    lots[:] = [l for l in lots if l["qty"] > 1e-12]
    return {"qty": sell_qty, "avg_basis": avg, "gain": gain}

Partial sell with average cost

Lots: 100 @ $1.00, 50 @ $2.00, 75 @ $1.50. Total: 225 units, total cost $312.50.

Average cost = $312.50 / 225 = $1.3889/unit

Sell 120 at $3.00: gain = (3.00 - 1.3889) * 120 = $193.33

After the sell, 105 units remain at the same $1.3889 average.

6. Special Events

Airdrops

Airdrops are treated as income at fair market value (FMV) on the date received. The FMV becomes the cost basis for future sales.

airdrop_lot = {
    "date": "2025-03-15",
    "qty": 1000,
    "cost_per_unit": 0.05,   # FMV at time of receipt
    "income_recognized": 50.0,  # 1000 * 0.05 reported as income
    "source": "airdrop"
}

Staking Rewards

Staking rewards are income at FMV when received (similar to airdrops). Each reward event creates a new lot.

staking_lot = {
    "date": "2025-04-01",
    "qty": 5.2,
    "cost_per_unit": 150.0,  # SOL price at receipt
    "income_recognized": 780.0,
    "source": "staking_reward"
}

Token Splits and Migrations

A token split or migration (old token to new token 1:1 or N:M) is generally not a taxable event. The total cost basis transfers to the new tokens.

def apply_split(lots: list[dict], split_ratio: float) -> None:
    """Apply a token split. split_ratio > 1 means more tokens."""
    for lot in lots:
        lot["qty"] *= split_ratio
        lot["cost_per_unit"] /= split_ratio

For a 1:10 split of 100 tokens @ $5.00: result is 1000 tokens @ $0.50. Total basis unchanged at $500.

7. LP Entry/Exit as Token Swaps

Entering an LP position is treated as selling the deposited tokens and receiving LP tokens. Exiting is the reverse.

LP Entry (deposit 10 SOL + 1500 USDC into SOL/USDC pool):

1. Dispose of 10 SOL at current FMV → capital gain/loss event
2. Dispose of 1500 USDC at current FMV → usually negligible gain/loss
3. Receive LP tokens with cost basis = FMV of deposited assets

LP Exit (redeem LP tokens for 12 SOL + 1400 USDC):

1. Dispose of LP tokens at FMV of received assets → capital gain/loss
2. Receive 12 SOL with cost basis = FMV at redemption
3. Receive 1400 USDC with cost basis = FMV at redemption

def lp_entry(sol_qty: float, sol_price: float, usdc_qty: float,
             lp_tokens_received: float) -> dict:
    """Model LP entry as disposal of component tokens."""
    total_value = sol_qty * sol_price + usdc_qty * 1.0
    lp_cost_basis = total_value / lp_tokens_received
    return {
        "disposals": [
            {"token": "SOL", "qty": sol_qty, "price": sol_price},
            {"token": "USDC", "qty": usdc_qty, "price": 1.0},
        ],
        "lp_lot": {"qty": lp_tokens_received, "cost_per_unit": lp_cost_basis}
    }

8. Multi-Hop Swaps

A multi-hop swap (e.g., SOL -> USDC -> TOKEN) creates multiple taxable events, one for each intermediate step. Jupiter often routes through intermediate tokens.

def multi_hop_events(hops: list[dict]) -> list[dict]:
    """
    Each hop is: {"sell_token", "sell_qty", "sell_price",
                  "buy_token", "buy_qty", "buy_price"}
    Each hop is a separate taxable event.
    """
    events = []
    for i, hop in enumerate(hops):
        events.append({
            "event": i + 1,
            "dispose": hop["sell_token"],
            "dispose_qty": hop["sell_qty"],
            "dispose_value": hop["sell_qty"] * hop["sell_price"],
            "acquire": hop["buy_token"],
            "acquire_qty": hop["buy_qty"],
            "acquire_basis": hop["buy_qty"] * hop["buy_price"],
        })
    return events

Example: Swap 1 SOL ($150) -> 150 USDC -> 10,000 TOKEN ($0.015 each)

• Event 1: Dispose 1 SOL (basis vs. $150 proceeds) → gain/loss on SOL
• Event 2: Dispose 150 USDC (basis vs. $150 proceeds) → usually ~$0 gain
• Result: 10,000 TOKEN with cost basis = $0.015/unit

9. Comparison View

The core value of this skill: run the same trade history through all five methods and compare total realized gain and estimated tax liability.

methods = ["FIFO", "LIFO", "HIFO", "Specific ID", "Average Cost"]
# After processing all trades through each method:
comparison = {
    "FIFO":        {"total_gain": 220.00, "tax_at_30pct": 66.00},
    "LIFO":        {"total_gain": 157.50, "tax_at_30pct": 47.25},
    "HIFO":        {"total_gain": 155.00, "tax_at_30pct": 46.50},
    "Specific ID": {"total_gain": 160.00, "tax_at_30pct": 48.00},
    "Average Cost":{"total_gain": 193.33, "tax_at_30pct": 58.00},
}
# HIFO minimizes liability in this example

See scripts/cost_basis_calculator.py for a full runnable comparison with realistic trade data including partial sells.

Quick Start

from scripts.cost_basis_calculator import CostBasisEngine

engine = CostBasisEngine()

# Add purchases
engine.add_buy("2025-01-10", "TOKEN", 100, 1.00)
engine.add_buy("2025-02-15", "TOKEN", 50, 2.00)
engine.add_buy("2025-03-01", "TOKEN", 75, 1.50)

# Sell and compare methods
results = engine.sell_compare("2025-04-01", "TOKEN", 120, 3.00)
engine.print_comparison(results)

Use Cases

1. Tax season preparation: Run your full year of trades through all methods before choosing one to report.
2. Accumulation strategy: Track partial sells during DCA accumulation, see how each method affects remaining basis.
3. LP position tracking: Model LP entry/exit as swaps and capture the associated gain/loss events.
4. Airdrop and staking income: Properly record income events and set cost basis for future disposals.
5. Multi-hop swap decomposition: Break down Jupiter routes into individual taxable events.

Files

Remember: The "best" method depends on your jurisdiction, your specific trade history, and your tax situation. This engine helps you compare — a tax professional helps you decide.