# Why expirables?
## Contract types
Contango is the expirable leader in DeFi. To understand why we need expirables, let's dive into the types of contracts available in CeFi:
* **Perpetual contracts -** Standardised **i**nstruments without an expiry date that can be held indefinitely and where funding fees are periodically exchanged between long and short on a regular basis, e.g. each 8h, to keep the futures price tethered to the spot price. These [funding rates](/exchange/resources/glossary.md#funding-rates) are unpredictable, i.e. depending on the market conditions you can receive or pay money. Over a longer-term horizon, funding fees can start biting into your profits, as high as 30% annualized ([Deribit insights](https://insights.deribit.com/market-research/perpetual-swaps-comparisons-and-findings/)). In a nutshell, you can't reliably control your costs with perpetuals.
* **Expirable contracts -** These instruments have [expiry dates](/exchange/resources/glossary.md#expiry-date), e.g. a monthly contract can be traded up to the end of the month. When a trader buys or sells a contract, all costs are known upfront.
The following table compares the main pros and cons of each contract type.
Perpetual futures
Expirable contracts
+
No expiration date
Control about the costs
-
No control about the costs
Expiration date
{% hint style="info" %}
In our opinion, we do not see perpetual and expirable contracts as competitors. Both are here to coexist: perps work well on a short time horizon where funding rates won't make a big dent in the position, whereas expirables are more suitable for longer-term trades.
{% endhint %}
## Market size
In CeFi **the total volume traded in 2021 was $112 trillions.** Expirable futures represent a small portion ($6.6 trillion), yet their volume kept growing in 2021 - about 2.4x compared to 2020 (source: [TokeInsight](https://s2.tokeninsight.com/static/levelPdf/TokenInsight_2021_Yearly_Crypto_Trading_Industry_Report_compressed.pdf)).
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