CECL forecasts and reversion

CECL covers the whole life of a loan, but nobody can forecast the economy for 10 or 20 years. ASC 326 solves that with a forecast period followed by reversion to history. This guide explains how long the forecast period should be, the reversion methods, and works through a five-year loan pool.

By Awais Jameel, Chartered Accountant. Reviewed by Muhammad Bilal, Chartered Accountant. 3 minute read.

Short answer

CECL forecast and reversion is how lifetime expected credit losses combine a reasonable and supportable forecast with historical loss information. For the period over which a company can make reasonable and supportable forecasts, it adjusts loss rates for expected conditions; beyond that period, ASC 326 requires it to revert to historical loss information, either immediately or on a straight-line or other systematic basis. In this guide's example, a $50,000,000 loan pool has lifetime CECL of $1,532,480 with straight-line reversion and $1,468,480 with immediate reversion.

At a glance

Forecast period
As long as forecasts are reasonable and supportable
Typical length
One to three years
Then
Revert to historical loss information
Reversion methods
Immediate, straight-line or other systematic
Not required
Discounting under the loss-rate method
Excel
CECL calculator
CECL forecasts and reversionForecast period: As long as forecasts are reasonable and supportable; Typical length: One to three years; Then: Revert to historical loss information; Reversion methods: Immediate, straight-line or other systematic; Not required: Discounting under the loss-rate method; Excel: CECL calculator.KEY FACTS AT A GLANCECECL forecasts and reversionForecast periodAs long as forecasts arereasonable andsupportableTypical lengthOne to three yearsThenRevert to historical lossinformationReversion methodsImmediate, straight-lineor other systematicNot requiredDiscounting under theloss-rate methodExcelCECL calculatorTax BakersCECL forecasts and reversionForecast period: As long as forecasts are reasonable and supportable; Typical length: One to three years; Then: Revert to historical loss information; Reversion methods: Immediate, straight-line or other systematic; Not required: Discounting under the loss-rate method; Excel: CECL calculator.KEY FACTS AT A GLANCECECL forecasts and reversionForecast periodAs long as forecasts are reasonable andsupportableTypical lengthOne to three yearsThenRevert to historical loss informationReversion methodsImmediate, straight-line or other systematicNot requiredDiscounting under the loss-rate methodExcelCECL calculatorTax Bakers
Key facts at a glance, as set out in this guide.

How do CECL forecast and reversion work?

For each year of the remaining contractual life, adjusted for prepayments, the company needs an expected loss rate. For the reasonable and supportable forecast period, the rate reflects its economic forecast, such as rising unemployment. After that, the rate reverts to the company's historical average, because there is no reasonable basis for forecasting further ahead. The reversion can be immediate, or gradual over a set period.

A CECL example with both reversion methods

A bank holds a $50,000,000 pool of five-year commercial loans that pays down by 20% a year. Its two-year forecast implies loss rates of 1.20% and 1.00%; its historical average is 0.60%. With straight-line reversion over one year, year 3 sits halfway between the last forecast rate and the historical rate.

YearBalanceRate, straight-lineLoss, straight-lineRate, immediateLoss, immediate
1$50,000,0001.20%$600,0001.20%$600,000
2$40,000,0001.00%$400,0001.00%$400,000
3$32,000,0000.80%$256,0000.60%$192,000
4$25,600,0000.60%$153,6000.60%$153,600
5$20,480,0000.60%$122,8800.60%$122,880
Lifetime$1,532,480$1,468,480
Annual loss rate: straight-line vs immediate reversionAnnual loss rate: straight-line vs immediate reversion11Year 111Year 211Year 311Year 411Year 5Straight-line, %Immediate, %
The two methods differ only in the year after the forecast ends.

The difference, $64,000, comes entirely from year 3. When forecasts are worse than history, straight-line reversion gives a larger allowance; when they are better, a smaller one. The CECL calculator (Excel) lets you switch methods and change the reversion period.

How long should the forecast period be?

As long as the company can support its forecasts with evidence, which for most banks is one to three years. ASC 326 does not set a length. The period should be consistent with the forecasts used for budgeting and capital planning, applied consistently, and changed only when the company's ability to forecast changes.

Whatever period is chosen, the reasoning should be written down with the evidence behind it, because auditors and regulators will ask why the forecast stops where it does and not a year earlier or later.

Which historical loss information is used?

Loss experience for assets with similar risk characteristics, over a period long enough to cover different economic conditions, adjusted for differences between the historical and current portfolio, such as underwriting standards or collateral. Some banks revert to a long-run average loss rate; others to the average over a specific lookback period.

How does IFRS 9 compare?

IFRS 9 works in a similar way: forecasts for the period that can be reasonably supported, then extrapolation, usually by reverting to long-run averages. The main difference is that IFRS 9 discounts expected losses and uses 12-month ECL for stage 1 assets. See forward-looking information in ECL and IFRS 9 vs CECL.

What are common mistakes with forecasts and reversion?

Changing the forecast period or reversion method each period to manage the allowance; using a historical loss rate from a short, benign period, so reversion pulls the allowance down too far; and applying forecasts to the full contractual life when they cannot be supported beyond the first year or two.

What must be disclosed?

The forecast period, the reversion method and period, and the factors that changed the estimate, as part of describing the methodology. Changes to the forecast period or reversion method are changes in accounting estimate, explained in the period they occur. See CECL methods and CECL disclosures.

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Questions people ask

What is the reasonable and supportable forecast period in CECL?

The period over which a company can support its economic forecasts with evidence, typically one to three years; ASC 326 does not set a length.

What does reversion mean in CECL?

Returning to historical loss information for periods beyond the reasonable and supportable forecast, immediately or on a straight-line or other systematic basis.

Is straight-line reversion better than immediate reversion?

Neither is required; straight-line avoids an abrupt step, immediate is simpler. The choice should be applied consistently.

Does CECL require discounting?

Not under the loss-rate method; a discounted cash flow method discounts at the effective interest rate.

Sources

Every fee, date and rule on this page was taken from these official and primary sources.

  1. FASB Accounting Standards Codification: Topic 326, Financial Instruments: Credit Losses
  2. Financial Accounting Standards Board

Rules and fees change. If you are reading this long after October 4, 2026, confirm the figures with the source before you rely on them.

ASC 326CECL methods: loss rate, vintage, PD/LGD, DCFASC 326CECL explained: current expected credit lossesECLCECL disclosures

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This guide is general information. It is not tax or legal advice for your situation.