Why Finance Retains Multiple Day Count Conventions

Summary

The document asks whether finance is likely to adopt one global day count convention and whether an existing convention could become the standard. The answer says a universal change is unlikely: conventions arose from established market practice, and replacing them would offer little benefit once contracts and systems already rely on them. A day count convention remains important for calculating interest and must be applied correctly, even if it is not a source of trading insight by itself.

Some conventions are more common in large markets, with Actual/360 given as an example, while standard contracts from industry bodies provide limited consolidation for interest rate swaps. The document’s conclusion is brief and conceptual rather than supported by market data or a survey. It offers no procedure for choosing a convention for a particular instrument, so practitioners still need to follow the contract and market convention relevant to the product.

Key ideas

• A single global day count convention is not expected to emerge.
• Conventions persist because contracts and market systems already depend on them.
• Some conventions are more common in major markets, but common use is not universal standardization.
• Industry standard contracts consolidate practice to a limited extent in interest rate swaps.
• Correctly applying the convention specified for an instrument remains essential.

Tags

# Towards a standard day count convention in Finance, what the standard should be?


# Towards a standard day count convention in Finance, what the standard should be?












I recently found out about the multitude of day count conventions in Finance (e.g.wikipedia and stackexchange). As far as I understand the reason for this variety is a long history of diverse usage.

Would I be correct to expect that in the (perhaps near) future a global standard will emerge? If so is there any of the current conventions a good candidate for a global standard?

## Answer by Phil H (score 4, accepted)

https://quant.stackexchange.com/a/35288

No.

It is a detail that is important to get right, but otherwise uninteresting. There is no point in changing a convention once you've set one. There are some more common ones associated with the biggest markets, like Act/360, but that's all.

Day count conventions are well documented. There is a degree of consolidation via ISDA standard contracts in the IRS market, but it is limited.

Shown in full with attribution under the source's licence. Licence: CC BY-SA 4.0 (Stack Exchange)

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.