Welcome to The S-Curve
Now you will be able to receive the latest announcements, product updates, and our insights on the mortgage market in real time.
The name of the blog, the S-Curve, is a reflection of our logo and the central feature of our prepayment model. S-curves are seen in nature in many phenomenon, from population growth to prepayment and default models. Our first S-curve, in the early 1990s, used the arctangent function, then piece-wise linear functions, and evolved over time to be more complex and vary by FICO, loan size and LTV. This evolution encapsulates both the timeless nature of fundamental relationships and constant innovation to describe them better over time.
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How Lowering Capital Costs Affects Higher Risk LoansThoughtsHow Lowering Capital Costs Affects Higher-Risk Loans
Government-sponsored enterprises (or GSEs) are companies that provide guarantees and financing to originators through the mortgage secondary market. The size and resilience of the GSE secondary market maximizes diversification and liquidity which reduces financial risk and cost of capital. This benefit accrues to conforming borrowers through lower mortgage rates and resiliently available financing.
Capital Safe Investments
One hundred years of the stock price performance of public utilities shows higher dividends, combined with lower returns and capital costs than an index of large companies. Theory indeed predicts that companies in protected markets would have lower income volatility that translates into lower stock price volatility and lower required returns.
This can be seen empirically by comparing two ETFs (exchange traded funds), XLU, the largest and oldest utility ETF, launched in 1998, versus SPY, the S&P 500 index. Since inception, XLU’s price return is about 130% (compared to SPY’s 280%), and its 10-year annualized return is 11% (compared to SPY’s 16%). However XLU pays a persistently higher dividend yield of 2.9% compared to 1.2% for SPY, and shows lower price volatility with a beta of 60%, compared to SPY’s beta of 100%. This is evidence that protected markets are safer havens to beat inflation with lower risk. Firms generally price to a 12%-15% return on equity, while regulated utilities generally price to 5-10% ROE. Even though ETFs are not individual companies, XLU and SPY’s performance have implications about GSE capital cost, which is the largest component of guarantee fees.
The Benefits of Lowering GSE Capital Costs
Fannie Mae and Freddie Mac (the GSEs) charge guarantee fees to compensate for the risk of guaranteeing and securitizing mortgages. These fees are included in the mortgage rate. The GSE guarantee conveys the lowest possible rate on mortgage backed securities through to borrowers. Lowering guarantee fees on higher-risk loans would lower mortgage rates and cumulatively, could save borrowers up to $3,000.
For example, for a $300,000 mortgage at 4%, the monthly P&I payment would be $1432. However, lowering the guarantee fee (and the mortgage rate) by 25 basis points lowers the payment $43 per month. This saves borrowers more than $3000 over seven years.
Lowering GSE capital costs to 6%-8% from 12%, could reduce guarantee fees by 25 bps for loans that require more capital without sacrificing financial resiliency. These borrowers are more likely to be lower-income, first-time homeowners or minority households. So, allowing the GSEs to retain federal backing as regulated utilities, and thus recognizing that GSE capital costs are lower than for fully private firms, can lower mortgage rates for higher risk loans which are more likely to be underserved populations.
Making Homeownership More Accessible to Lower-Income Families and Underserved Groups
Homeownership is the largest source of inter-generational wealth for working- and middle-class families, and the gateway is access to a mortgage. Especially for those whose access to homeownership has historically been hindered, financial security is enhanced by affordable credit. This regulated utility framework shows that the right public-private combination can focus enduring benefits on underserved communities to help build credit and long-term financial stability. National standards and lower mortgage rates help avoid predatory lending and never-ending debt — so that these households have a better chance to thrive in the financial marketplace.
Building wealth in underserved communities can begin by boosting individual wealth and lead to more local commercial activity. This can start the flywheel of positive economic community feedback that middle class and white neighborhoods are accustomed to.
As the largest mortgage financing provider, the GSEs have repeatedly shown resilient presence in the market in sharp contrast to mortgage segments that are not federally backed. They now operate more like regulated utilities and intermediate most risk into the public capital markets with an effective regulator setting standards for capital, credit and returns. The final component is to recognize their lower cost of capital and thus allow guarantee fees and mortgage rates to reduce accordingly.
The S-Curve Archives
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ThoughtsRecently, aggregators have crossed market borders by issuing residential mortgage-backed securities (RMBS) backed by owner-occupied (OO), GSE-eligible conforming loans. Additionally, conforming mortgage loans have drawn investment interest from insurance companies fronted by aggregators and evaluated by third-party firms. These developments constitute historically rare disintermediations of the nearly monopsonist purchases of conforming loans by the GSEs.
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PodcastJoin Rob Landauer in a conversation with Abe Martin as they discuss his recent Pipeline article, "Modeling the Balance Behavior of HELOC Borrowers." In this episode, they highlight key points from the article as he shares insights into the draw component of HELOCs and provide an update on the beta rele
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News
We’re excited to announce a major addition to the Andrew Davidson & Co., Inc. (AD&Co) team. Industry leaders Kelli Sayres and Gene Park, known for building and scaling leading fixed-income analytics platforms, have joined AD&Co’s Business Development team.
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ThoughtsBuilding on our earlier research on expanded consumer attributes, AD&Co continues to explore how credit data contributes to modeling delinquency and prepayment risk, which are key drivers of mortgage servicing rights cash flows and valuation.
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EventsAndrew Davidson recently joined NFM Lending’s Greg Sher on the One On One podcast to discuss our recent white paper, “The Impact of Moving Away From the Tri-Merge Standard.”
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EventsAD&Co recently sponsored and attended SFVegas 2026 and Optimal Blue Summit 2026. This post shares the AD&Co team's unique perspectives and key takeaways from attending both conferences.
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NewsAD&Co US Mortgage High Yield Indices
The Federal Reserve Economic Data (FRED) portal, housed by the Federal Reserve Bank of St. Louis, has been publishing AD&Co’s CRT indices since 2019. These series posted under the overall name of “US Mortgage High-Yield” include total return rates and credit and option-adjusted spreads (crOAS) – a projected return’s spread over Treasury (in the past, Libor). These series are available going back to 2014-end and tiered by CRT initial supports.
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ThoughtsIn July 2025, the US Federal Housing Finance Agency (FHFA) announced that the government-sponsored entities (the Enterprises or GSEs), Fannie Mae and Freddie Mac, would permit lenders to choose between Classic FICO and VantageScore 4.0 credit score models for loans sold to the GSEs. FHFA also stated in a social media post that the tri-merge standard would be maintained for mortgage underwriting. Nevertheless, some mortgage industry stakeholders recommend moving away from the tri-merge standard for GSE mortgages in favor of a single or bi-merge report standard.
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News
As housing faces more climate threats that result in more losses, the insurance program that it sits on is teetering on the brink of collapse. Yet, the home insurance market has three distinct stakeholders that have competing priorities, and today, there is no motivation for a collaborative solution.
Understanding how to strengthen and protect the current structure requires looking at the cost burdens along with the risk for each of those parties.
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ThoughtsThere has been a flurry of activity in the mortgage markets since the 2018 passage of the Economic Growth, Regulatory Relief, and Consumer Protection Act. This act requires the Federal Housing Finance Agency (FHFA, now known as US Federal Housing) to validate and modernize the credit score models used in the housing finance system. It should be noted that so far, the discourse has been around mortgages sold to the Enterprises (Fannie Mae and Freddie Mac). Ginnie Mae has not provided any guidance on their plans to start using new credit score models.