If you are weighing a fixed index annuity, the quote or brochure will probably list a cap, a participation rate or a spread, and it will often show the index’s past performance beside them. The index’s gain is only the starting number. How index annuity interest is calculated depends on a sequence: measure the index change over a set period, apply the insurer’s crediting method to that change, then apply the contract’s floor.
This article runs one hypothetical index gain through each of the three methods so you can see the arithmetic. Every number below is made up to keep the math easy to follow. None of them are typical or current rates, and none come from a real product.
Why an index annuity’s credited interest is not the index return
A fixed index annuity does not invest your premium in the index. The insurer holds your money in its general account, and the contract promises to credit interest based on how an index changes over a defined period. You never own index shares, and the index’s gains do not pass straight through to you.
Two things sit between the index and your account. The first is the crediting method, which is the formula that converts the index change into a percentage of interest. The second is the floor, usually 0% in the contracts people compare, which sets the lowest interest the contract can credit for a period.
Many indexes tracked in these contracts are price indexes, which leave out dividends. If that is the case in your quote, the index change used in the formula is smaller than the total return an investor in the underlying stocks would see. Check which version of the index the contract uses.
The crediting period and the index change: where every calculation starts
The crediting period is the stretch of time over which the contract measures the index. One year is common, and some contracts use two, five or more years. The contract credits interest at the end of each period, usually on a contract anniversary.
The simplest way to measure the change is annual point-to-point. The contract records the index level on the first day of the period and again on the last day, and the change is the percentage difference between the two.
Here is the example used for the rest of this article:
- Premium: $100,000
- Index level at the start of the period: 5,000
- Index level at the end of the period, one year later: 5,400
- Index change: (5,400 − 5,000) ÷ 5,000 = 8.0%
Anything that happens in between, such as the index reaching 5,700 in the summer and falling back, does not matter under point-to-point. Only the two recorded levels count.
How index averaging changes the starting number
Some contracts measure the change differently. Under monthly averaging, the contract records the index level every month, averages the twelve readings, and compares that average to the starting level. Suppose the twelve readings in our example average 5,200. The index change is then (5,200 − 5,000) ÷ 5,000 = 4.0%, even though the year ended 8.0% higher.
Averaging lowers the measured gain when the index climbs steadily, because early readings sit near the starting level. It can also raise the measured change when the index rises early in the year and then drops back. Averaging usually appears together with a different cap, participation rate or spread than a point-to-point option, so the method and the rate need to be compared as a pair.
The three methods below take the 8.0% point-to-point change as their input.
How a cap works, with a worked example
A cap is the maximum interest the contract will credit for the period. If the index change is above the cap, the contract credits the cap. If it is below, the contract credits the index change.
Take a hypothetical 6% cap:
- Index change: 8.0%
- Cap: 6%
- Credited interest: 6% (the lower of the two)
- On $100,000: $6,000
If the index had risen only 4.0%, the contract would credit 4.0%, or $4,000, because the change is under the cap. The cap only affects years when the index does better than the cap rate.
A cap trades away the large gains for a clear ceiling. In a strong year, everything above the cap stays with the insurer.
How a participation rate works, with the same example
A participation rate is the share of the index change the contract credits. A 60% participation rate credits 60 cents of interest for every 1% the index gains.
Using the same 8.0% change:
- Index change: 8.0%
- Participation rate: 60%
- Credited interest: 8.0% × 0.60 = 4.8%
- On $100,000: $4,800
The effect scales with the index change. At a 4.0% index gain, the credit is 2.4%. At a 15% gain it is 9.0%. Because a participation rate on its own sets no ceiling, there is no point at which extra index gains stop counting, which is the main difference from a cap.
Some contracts combine methods, for example a participation rate with a cap on top of it. If a quote lists both, apply the participation rate first and then check the result against the cap. Confirm the order with the carrier, since the contract wording governs.
How a spread (or margin) works, with the same example
A spread, sometimes called a margin or asset fee, is a percentage subtracted from the index change. Whatever is left is the credited interest.
With a hypothetical 3% spread:
- Index change: 8.0%
- Spread: 3%
- Credited interest: 8.0% − 3.0% = 5.0%
- On $100,000: $5,000
If the index gains less than the spread, the subtraction would produce a negative number, and the floor takes over. At a 2% index gain and a 3% spread, the credit is 0%, not negative 1%. You are not charged the shortfall, though you receive no interest that period.
Because the spread is a fixed subtraction, it takes the same bite from a small gain as from a large one, but a small gain loses a bigger share of its value. Three points taken from an 8% gain leaves 5%, which is 62.5% of the gain. Three points taken from a 4% gain leaves 1%, which is 25% of it.
Same index gain, three different credits: a side-by-side comparison
All three methods take the same input and return different results, and the ranking between them changes with the size of the gain. The table below uses the made-up terms from above (6% cap, 60% participation rate, 3% spread) on a $100,000 premium. The final row shows what happens when the index falls, which is covered in the next section.
Index change 6% cap 60% participation 3% spread +2% 2.0% ($2,000) 1.2% ($1,200) 0% ($0) +4% 4.0% ($4,000) 2.4% ($2,400) 1.0% ($1,000) +8% 6.0% ($6,000) 4.8% ($4,800) 5.0% ($5,000) +15% 6.0% ($6,000) 9.0% ($9,000) 12.0% ($12,000) −10% 0% ($0) 0% ($0) 0% ($0)
Three patterns show up:
- The cap credits the most in modest years and falls behind in strong ones.
- The participation rate credits less than the cap in small and moderate years and more once the index change passes 10%, where 60% of the gain exceeds the 6% cap.
- The spread credits least in small-gain years and the most in large-gain years, since its fixed deduction matters less as the gain grows.
None of the three is better in general. Which one credits more depends on the rate each contract sets and on how the index performs, and no one can know that in advance. A cap of 6% and a spread of 3% are not equivalent offers, and neither is comparable to a participation rate of 60%, until you test them against several index outcomes the way the table does.
What happens when the index falls, and what the floor does and does not protect
In the table, a 10% index drop produces a 0% credit under every method. That is the floor at work. If the contract has a 0% floor, a falling index does not reduce the interest already credited to your account for that period’s index movement.
The floor protects the index-linked credit. It does not protect against everything that can reduce what you receive:
- Surrender charges. Withdrawing more than the contract allows during the surrender period typically triggers a charge, which can reduce your payout even when no index loss occurred.
- Rider fees. If you add a benefit rider, such as an income rider, its fee is often deducted from the contract value regardless of index performance. A 0% credit with a rider fee can lower the account value.
- Market value adjustments. Some contracts apply an adjustment to early withdrawals that can move up or down with interest rates.
- Zero-credit periods. A 0% floor means a flat year, with no interest added. Over several flat years the opportunity cost can be real, since inflation keeps reducing what the money buys.
Also check whether the contract applies the floor at the end of each crediting period or over a longer term. A contract that measures a multi-year period gives you nothing until that period ends, and withdrawals before the end may forfeit the credit for that period. The contract’s crediting provisions say how it handles that case.
Can the insurer change these numbers? Renewal rates and what to check in the contract
In most index annuities, the insurer can reset the cap, participation rate or spread when a crediting period renews. The rate in a quote may be guaranteed for the first period only. After that, the carrier declares new rates, typically before the next period starts, and the contract states the limits on how far they can move.
Look for these items in the contract and its disclosure documents:
- Guaranteed minimums and maximums. A contract may promise that the cap never goes below a stated level, or that the participation rate never falls below a stated percentage. Without that guarantee, the carrier’s range is wider.
- How long the initial rates last. Some are fixed for one period, others for longer.
- The notice you get before renewal. Find out when the new rates are communicated and whether you have a window to reallocate between crediting options.
- The index and its replacement terms. The contract may allow the insurer to substitute a different index under stated conditions. Read what those conditions are.
- Your options if rates drop. Ask whether moving to another account or surrendering is possible without a charge at renewal, or whether surrender charges still apply.
Because the carrier’s own ability to pay is what stands behind the credited interest, it also helps to know how to read its financial strength ratings. Our post on what AM Best, Moody’s and S&P ratings tell you about an annuity company covers that side of the decision.
Questions to ask before you compare two index annuity quotes
Two quotes can look similar and credit very different amounts, so the terms need to be lined up before the comparison means anything. These questions go to the agent or, better, to the carrier in writing:
- Which crediting method does each option use? Annual point-to-point, monthly averaging, monthly sum or another method.
- How long is the crediting period? One year, two years, five years or longer, and when interest is credited.
- What are the cap, participation rate and spread for each option, and are they combined? Ask whether a participation rate is paired with a cap.
- Are the rates guaranteed, and for how long? Ask for the guaranteed minimum cap or participation rate and the lowest rate the contract permits.
- Which index is used, and does it include dividends? Price-return indexes and total-return indexes behave differently.
- What is the floor, and does it apply to each period? Confirm that it is 0% and that no charge is subtracted from credited interest.
- What fees and charges apply regardless of the credit? Rider fees, surrender charges and any market value adjustment.
- What happens if I withdraw mid-period? Ask whether interest for the current period is credited in part, in full or not at all.
- How are credited interest and the index start level handled at the next period? Confirm whether credited interest locks in and the next period begins at the new index level.
- Can I see an illustration, and what does it assume? Hypothetical illustrations assume particular index performance. Ask for the assumptions in writing and for results under flat and falling index scenarios as well as rising ones.
Ask each carrier for the same set of figures, then run both through the table method used in this article with the same hypothetical index changes. The contract that credits more in a 4% year may credit less in a 15% year, and your comparison should show you both.
Apply it to your own quote
Take the side-by-side example from this article and apply it to the crediting terms in a quote you already have: calculate the credit at +2%, +4%, +8%, +15% and −10%, then use the questions in the last section to check the terms with the agent or the carrier. Our guide on how to compare different annuity products is a good next read.