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Selecting QuantLib Rate Helpers by Instrument Type

Article Quant Q&A · Author: FRANK Zhu
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Summary

The document explains how to choose among QuantLib’s deposit, FRA, and swap rate helpers when constructing an interest-rate term structure. The key rule is to match a helper to the instrument represented by the market quote, rather than selecting it solely from the quote’s tenor. A short quote can still be a swap quote and should then be represented with a swap helper; deposits, FRAs, and swaps each have distinct pricing mechanics.

The response also notes that the standard SwapRateHelper models an older style of vanilla swap with LIBOR against a fixed rate. If the market quotes instead represent overnight index swaps, such as those tied to term SOFR in the question’s image, an OIS helper may be appropriate. The responder is uncertain about the instrument identification because the image is not readable to them. The guidance is conceptual and does not provide construction code, conventions, or a complete curve-building example.

Key ideas

  • Choose a QuantLib rate helper based on the quoted instrument, not just its maturity.
  • Deposit, FRA, and swap helpers implement the pricing conventions of different instruments.
  • A short-tenor quote may still require a swap helper if it represents a swap.
  • The standard SwapRateHelper refers to a LIBOR versus fixed-rate vanilla swap.
  • Overnight index swap quotes may call for OISRateHelper, subject to identifying the instrument correctly.

Tags

Fixed incomeDerivatives pricing
Full text
# DepositRateHelper vs SwapRateHelper vs FraRateHelper in QuantLib


# DepositRateHelper vs SwapRateHelper vs FraRateHelper in QuantLib












I'm new to QuantLib and am trying to build a term structure for a vanilla IRS. I understand that QuantLib provides several helper functions like `DepositRateHelper`, `SwapRateHelper`, and `FraRateHelper` to help with this, but I'm not entirely sure when to use each one.

From what I’ve gathered online:

- For short tenors (in days), I should use `DepositRateHelper`

- For middle-length tenors (in months), use `FraRateHelper`

- For longer tenors (more than 1 year), use `SwapRateHelper`

Is this understanding correct? For instance, in the Bloomberg screenshot below, would I use `FraRateHelper` for the month tenors (1MO-11MO) and `SwapRateHelper` for the longer tenors (12MO-50YR)?

Could someone explain what's happening behind these functions and clarify when each should be used?

Thank you!

## Answer by Luigi Ballabio (score 2)

https://quant.stackexchange.com/a/80920

Deposits, FRA and swaps are different instruments; you can get better definitions of them by searching than those I could write here. Each instrument is priced differently, and each of DepositRateHelper, SwapRateHelper and FraRateHelper does the specific calculation for the relevant instrument.

So no, it's not just a matter of maturity; if, for instance, the quote you're getting is for a swap, you'll have to use SwapRateHelper even if the tenor is short.

Also, SwapRateHelper refers to old-style vanilla swaps paying LIBOR vs a fixed rate. I see "term SOFR" in your image, so I'm guessing that these are OIS instead, which means you'll need OISRateHelper. I can't be sure, though, since I don't read Chinese.

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.