What is the Monthly Sum Option in a Fixed Indexed Annuity

Monthly sum and monthly average sound like two flavors of the same idea, and that similarity causes real confusion — but they’re built on completely different math, and the difference matters more than the names suggest. Monthly average takes twelve index readings and averages them against the starting value, the same gentle smoothing logic as daily average, just sampled less often. Monthly sum does something else entirely: it calculates twelve separate month-over-month percentage changes, caps each positive one individually, lets every negative one pass through in full, and adds the whole stack together. That asymmetry — capped gains, uncapped losses — is what defines this method, and it’s also why more than one independent source describes monthly sum as the most volatile of the common crediting approaches, not the mildest.

Jason Stolz, CLTC, CRPC, DIA, CAA, is Chief Underwriter at Diversified Insurance Brokers and has walked enough clients through this specific method to know it’s the one most likely to be misunderstood on first read, precisely because “monthly” sounds gentle. As an independent annuity broker working across the full carrier landscape, our office can show you exactly how a monthly sum strategy would have performed against real historical monthly data before you commit to it, rather than leaving you to discover the capped-gains-versus-uncapped-losses dynamic after a difficult year.

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Figures above are illustrative only and don’t represent any specific product, index, or currently offered rate.

The Mechanic, Precisely

A monthly sum strategy, sometimes called monthly point-to-point, records the index value at the start and end of each calendar month within the crediting period, typically on the same day-of-month the contract was issued. For each of the twelve months, the insurer calculates the percentage change from that month’s starting value to its ending value. If the result is positive, it’s compared against a monthly cap — a much smaller number than an annual cap, commonly in the range of one and a half to three percent — and limited to that cap if it exceeds it. If the result is negative, no cap applies at all; the full loss is recorded exactly as it occurred. At the end of the twelve months, all twelve results, capped positives and uncapped negatives alike, are added together. If that sum is positive, it’s credited as the year’s interest, subject to whatever additional adjustment the contract specifies. If the sum is zero or negative, the standard annual floor applies and 0% is credited for the year — your principal is never reduced, but a bad enough stretch can erase an otherwise strong year’s worth of capped gains entirely.

The Real Story: Capped Gains, Uncapped Losses

The first row of the table above is the scenario that actually defines this crediting method, and it’s worth sitting with. Eleven months of solid, capped gains add up to 16.5% — a genuinely strong run by any measure. Then one difficult month, a single sharp decline, counts at its full, uncapped value and wipes out not just that month’s contribution but a meaningful share of everything the prior eleven months built. The final sum goes negative, the annual floor takes over, and the credited result for the entire year is zero. This isn’t a freak edge case; it’s the structural consequence of a design where gains are limited every single month but losses never are, and it’s exactly the dynamic that shows up in real historical index data more often than the phrase “monthly sum” suggests it might.

Why This Is Actually the More Volatile Choice, Not the Gentler One

Given how similar the name sounds to monthly averaging, it’s a reasonable assumption that both methods sit on the same “smoother, steadier” end of the spectrum as daily averaging. They don’t. Monthly average and daily average both compare a single averaged value against a starting point, which mechanically dampens extremes in either direction. Monthly sum does the opposite of dampening on the downside — it counts every bad month at full strength while still limiting every good month — which is precisely why more than one independent analysis of these crediting methods describes monthly sum as the most volatile of the common approaches in terms of actual credited outcomes, with monthly averaging producing the steadiest results of the three regardless of how the market actually behaves. The name suggests gentleness. The math does not always deliver it.

Where It Can Genuinely Outperform

The second row of the table above shows the other side of this design, and it’s a real advantage, not a marketing gloss. Because each of the twelve months gets its own fresh cap allowance rather than a single cap applied to the whole year’s move, a market that grinds upward in modest, consistent monthly increments — never triggering the monthly cap, never suffering a serious down month — can produce a credited total that exceeds what a single annual cap would have allowed under a point-to-point design measuring the same underlying climb. Twelve months of 1.5% gains, each safely under a 2% monthly cap, sum to 18%, a result a 9% or 10% annual cap simply couldn’t match. This is the scenario monthly sum is actually built for: steady, distributed, low-drama growth with no sharp reversals along the way.

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One Feature Worth Asking About Directly

A small number of contracts include a monthly floor, often set at 0%, that prevents an individual month’s decline from being counted below that floor in the running sum — effectively capping the downside on a per-month basis the same way the upside is capped. This isn’t the standard design; most monthly sum strategies count negative months at their full, uncapped value exactly as described above. But where a monthly floor genuinely exists, it changes the entire risk profile of this method for the better, since the exact scenario in the first row of the table above becomes structurally impossible. If a monthly sum strategy is genuinely on the table for you, confirming whether a monthly floor applies, rather than assuming the standard uncapped-losses design, is one of the single most consequential questions to ask before choosing it.

Monthly Sum vs. Monthly Average: The Distinction That Actually Matters

These two methods get confused constantly because of the name, so it’s worth stating the difference in one place plainly. Monthly average takes twelve index values, averages them, and compares that single average to the starting value — one comparison, one result, dampened in both directions. Monthly sum takes twelve separate percentage changes, caps each positive one individually, lets negatives through uncapped, and adds all twelve results together — twelve separate comparisons, each with its own cap, summed rather than averaged. The two methods can produce meaningfully different credited amounts from the exact same underlying index path, and neither is simply a variation of the other. Our broader look at indexed annuity crediting methods covers monthly average and the rest of the menu alongside this one.

How the Crediting Period Applies

Monthly sum runs on a crediting period exactly like every other strategy described on this site — commonly one year, defining the twelve months that get measured and summed. Our full explanation of how a crediting period actually works covers what happens at renewal and what your options look like if you need to access funds before a period completes, both of which apply to monthly sum exactly as they would to any other method.

Where This Fits Among the Broader Menu

Monthly sum is one entry among several on most fixed indexed annuities. Our overviews of cap rates, participation rates, and spread rates cover the formulas most often paired with a monthly cap, and our comparison of monthly sum against daily averaging is worth reading directly alongside this page, since the two sit at opposite ends of the risk spectrum despite both being built around monthly or daily sampling.

Who Genuinely Fits This Strategy

A buyer who has real conviction in a steady, distributed, low-volatility upward market, and who has specifically confirmed how the contract treats negative months, is the clearest fit for monthly sum. It rewards a market that behaves in a very particular way — no sharp reversals, no single catastrophic month — and it penalizes almost any market that doesn’t behave that way more severely than the alternatives on this page. It fits poorly for a buyer who hasn’t confirmed whether a monthly floor applies, or who assumed “monthly” implied a gentler, more averaged design similar to monthly or daily averaging. This is not a strategy to select based on the name alone.

How We Help

We walk through the actual monthly cap, whether a monthly floor applies, and how a specific monthly sum strategy would have performed against real historical index data before recommending it — because the gap between what this method sounds like it does and what it actually does is wider than for almost any other crediting formula on the market. If a monthly sum strategy genuinely fits your outlook, we’ll help you understand exactly what you’re accepting in exchange for its upside.

Our broader guidance on choosing the right annuity and genuine annuity suitability reflects the same discipline we bring to this comparison. If you already hold an indexed annuity and have never confirmed which crediting method your allocation actually runs on, our second-opinion review is built for exactly that question, and if the answer points toward a different contract entirely, our guide on replacing an annuity the right way walks through that decision honestly.

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