Definition
Monthly sum crediting is an indexed annuity calculation method that measures the index's percentage change in each month of a crediting period, applies a monthly cap to each positive month, leaves negative months uncapped, and sums the twelve resulting figures to produce the period's index gain.
Why it matters
Monthly sum is the calculation method whose behavior diverges most clearly from point-to-point under the same index conditions — by capping each upward month while leaving downward months uncapped, it produces credits that are highly sensitive to index volatility. Naming the method directly is what makes it possible to characterize the structural asymmetry it embeds. A single sharply negative month can fully offset multiple capped positive months, producing a zero credit even on years where the index rose meaningfully start to end.
How it works
In monthly sum crediting, each month's index return is calculated, and any month whose return is positive is capped at a monthly cap rate (commonly in the 1.5% to 3% range, though terms vary). Months with negative returns are not capped — the full negative is included in the sum. The twelve capped-and-uncapped monthly figures are summed; if the total is positive, it is the period's index gain (subject to any participation rate or floor adjustments under the contract); if the total is zero or negative, the credit for the period is zero (the indexed-annuity floor protects against negative crediting at the contract level). The structure produces a credit only when the sum of capped positives exceeds the sum of uncapped negatives, which happens reliably in low-volatility upward markets but can fail in markets with even modest downside volatility.
In practice
For an individual evaluating an indexed annuity that offers monthly sum as one of its crediting strategies, the operative question is how the strategy is expected to perform across realistic index-return paths. A monthly sum strategy with a 2% monthly cap can produce up to roughly 24% in a smoothly rising market but can produce zero in a market that rises overall but includes one or two negative months below the capped level. A professional should provide a back-test of the strategy across recent historical periods that include realistic volatility, not just calm upward periods. Monthly sum is structurally most attractive in low-volatility environments and structurally least attractive in volatile ones; the contract's choice of available strategies and the reader's expectations about future market conditions are what determine whether monthly sum is the right structure within an indexed-annuity allocation.
In the Longevity Standard Framework
Monthly sum crediting is supporting vocabulary in the Longevity Standard framework — a calculation-method component of the crediting parameter drag cost structure that produces particularly volatility-sensitive results. Crediting parameter drag is one of five values that the cost-structure claim property can take, alongside none, explicit fee, embedded spread, and guarantee charge. The cost-structure property determines how much of the structural pooling benefit reaches the participant; in monthly sum strategies, the asymmetric treatment of capped positive months and uncapped negative months means the relationship between underlying index behavior and credited return is highly path-dependent and is materially different from the point-to-point calculation method on the same index.
Related terms
- Point-to-point crediting
- Daily averaging
- Cap rate
- Participation rate
- Spread (crediting)
- Annual reset
- Index crediting strategy
- Fixed indexed annuity