Understanding the MV/BV Ratio: Implications for Plan Design

A practical guide to interpreting the market-value-to-book-value ratio in stable value funds — explaining what it measures, why it matters for plan fiduciaries, how it behaves through interest rate cycles, and what actions are available when ratios deteriorate.

# Understanding the MV/BV Ratio: Implications for Plan Design

## What the MV/BV Ratio Measures

The market-value-to-book-value ratio is the single most important indicator of a stable value fund's financial health. It measures the relationship between two values: the market value of the fund's underlying fixed income portfolio (what those securities would fetch if sold today at current market prices) and the book value of the fund (the stable $1.00-per-unit price at which participants transact). A ratio of 1.00 means the portfolio's market value exactly equals its book value. A ratio above 1.00 indicates that the portfolio is worth more in the market than participants' book value accounts — a surplus providing cushion. A ratio below 1.00 indicates that participants' book value accounts exceed what the portfolio could be sold for — the wrap providers are making up the difference through their contractual guarantees.

## How the Ratio Moves Through Rate Cycles

The MV/BV ratio is primarily driven by interest rate movements. When rates rise, fixed income bond prices fall, reducing the market value of the portfolio while book value continues to accrue at the existing crediting rate. The ratio falls. When rates fall, bond prices rise, increasing market value relative to the stable book value. The ratio rises.

The magnitude of the ratio's movement depends on the portfolio's duration. A portfolio with a 4-year effective duration will see its market value decline by approximately 4 percent for each 100 basis point increase in rates — and rise by a similar amount for each 100 basis point decline. During the 2022 rate cycle, when the Federal Reserve raised rates by more than 500 basis points over 18 months, stable value funds with typical intermediate durations saw MV/BV ratios fall from near 1.00 to trough levels of 0.88 to 0.94 across most of the industry.

The ratio recovers over time as the portfolio earns its way back to parity — as maturing bonds are reinvested at higher current yields, the portfolio's book yield rises, driving higher crediting rates. The speed of this convergence depends on portfolio duration: a shorter-duration portfolio turns over faster and converges more quickly, while a longer-duration portfolio generates more yield pickup but converges more slowly.

## Why the Ratio Matters for Plan Fiduciaries

For plan sponsors, the MV/BV ratio has two primary implications. First, it is the primary indicator of whether the fund's wrap providers are bearing real economic exposure — and therefore whether the credit risk to those providers is material. A fund with a ratio of 0.90 means wrap providers are on the hook for 10 cents per dollar of participant account balance if all participants demanded market value redemptions simultaneously. Monitoring wrap provider financial strength relative to this exposure is a fiduciary obligation.

Second, the ratio affects the crediting rate. The Buckingham crediting rate formula incorporates the MV/BV ratio as a key input — funds with lower ratios will, all else equal, earn lower crediting rates over time as the formula works to close the gap. This means that participants who observe a declining MV/BV ratio can expect some crediting rate compression in the near term, even as the underlying portfolio is now earning higher market yields on new investments.

## Wrap Contract Termination Floors

Most wrap contracts include termination provisions triggered if the MV/BV ratio falls below a specified floor — typically 0.75 to 0.85. Below this floor, the wrap provider has the right to terminate the contract and cease providing book value coverage. Understanding these floor levels and monitoring the margin of safety above them is critical fiduciary practice.

## Actions Available When the Ratio Deteriorates

When the MV/BV ratio deteriorates, plan sponsors and managers have limited but meaningful tools. Duration reduction — selling longer-duration bonds and reinvesting in shorter-maturity securities — reduces further market value exposure to additional rate increases, but crystallizes the existing gap by selling securities at their current depressed prices. Increasing crediting rates gradually (within the formula's constraints) to attract additional participant inflows can dilute the negative MV/BV position by bringing in new book value at closer to market value. Maintaining wrap provider relationships and communicating proactively about the portfolio's position is critical during periods of stress.

The most important discipline is prospective: conservative duration management during benign rate environments creates a larger margin of safety before reaching distressed MV/BV territory. Funds that maintained shorter portfolio durations entering 2022 weathered the rate shock with meaningfully higher MV/BV ratios than those with longer portfolios.