# Costs

> Fees read the non-promotional tier, and cost is checked before anything else because most ideas die here.

## Check costs first

```
cost_model_refresh()
cost_breakeven(trades_per_day=20)
```

This is step one of the [order of work](/docs/workflow), before data ingest
and long before any statistics. The reason is arithmetic.

At the published Coinbase Exchange entry tier — **60 bps taker per side**,
non-promotional, so a **120 bps round trip** — twenty trades a day costs:

```
120 bps × 20 trades/day × 365 days / 100 = 8,760% per year
```

No signal fixes that. An idea requiring 20 trades a day at the entry tier is
dead before it is tested, and finding that out costs one tool call rather
than a week of backtesting and a chunk of your trial budget.

The fee is named explicitly so the figure can be audited and recomputed
against your own cost model rather than taken on trust.

## Non-promotional tiers, on purpose

Fees read `fee_tier_without_promotion.current_tier`, not the promotional
`fee_tier` object.

Promotional rates expire. A backtest priced against a promotion is a backtest
of a business relationship rather than of a strategy, and it will look worse
the moment the promotion ends — which is exactly when you would be trading it
live.

## Prices and fees describe the same venue

Candles come from Coinbase **Advanced Trade** (350 bars per request), not
Coinbase Exchange. Earlier versions pulled candles from Exchange while
reading Advanced Trade fees, which meant prices and fees described two
different products. `gate_check` warns on a mismatch.

## Staleness

The cost model carries a one-hour staleness horizon. `server_status` reports
`age_seconds` and `source` for every cost model, so an old model is visible
as old.

A **fallback** ladder — the hardcoded table used when no API key is
configured — reports its `fetched_at` as when the table was assembled, not
when anything was retrieved. Refreshing a fallback returns the same table, so
it is reported as old rather than as stale: "stale" means *refresh this*, and
there is no refresh that would help.

## Fee share of returns

`backtest_result` reports gross and net side by side, plus the fee share of
gross return. A strategy whose fee share is above 100% is not a marginal
strategy; it is a fee-generation mechanism.

## Breakeven hit rate

```
stats_triple_barrier(...)
```

Triple-barrier labelling reports a breakeven hit rate — the win rate you
would need for the strategy to break even after costs. When barriers are
tighter than the round-trip fee, this **exceeds 1.0**, meaning no achievable
hit rate is sufficient. That is a complete answer, and it arrives before any
model is fitted.