How to Calculate Your Long-Term Disability Income Gap Before It Costs You Everything

Your Disability Income Gap Is Not the Same as Your Salary Replacement Rate

The income gap is the dollar difference between what you actually receive monthly during a disability and what you actually spend. These two numbers are rarely what you expect.

Most people anchor to their salary. That's the wrong starting point. Your LTD policy pays a percentage of your base salary. It excludes bonuses, RSUs, commissions, and employer 401(k) contributions. It applies a benefit cap. Then the IRS may tax the benefit if your employer paid the premiums.

The correct formula:

Monthly Income Gap = Monthly Essential Expenses minus (Monthly LTD Benefit after tax) minus (Monthly SSDI Benefit, if approved)

Work through each component before assuming you're covered.

Step 1: Establish Your Monthly Essential Expenses

Your income gap target is not your gross income. It is the minimum monthly cash outflow required to keep your household solvent during a multi-year disability.

Tally these categories:

• Housing: mortgage or rent, property taxes, HOA fees
• Debt service: auto loans, student loans, personal loans
• Insurance premiums: health, auto, homeowners or renters
• Food, utilities, and basic transportation
• Childcare and education obligations
• Minimum investment account contributions you cannot defer

Exclude discretionary spending. Disability changes behavior. You will cut restaurants, travel, and entertainment. You will not cut your mortgage.

Example. A household in Austin, Texas carries a $3,200 monthly mortgage, $900 in debt service, $1,400 in health insurance and other premiums, $1,100 in food and utilities, and $1,200 in childcare. Total monthly essential expenses: $7,800.

Step 2: Calculate Your After-Tax LTD Benefit

Your employer's group long-term disability policy is the starting point. Read the plan document. You need two specific numbers: the benefit percentage and the monthly benefit cap.

The gross monthly LTD benefit formula:

Gross Monthly LTD Benefit = (Annual Base Salary / 12) x Benefit Percentage, subject to the plan's monthly cap

Then determine taxability. If your employer pays the premiums and does not include the cost in your W-2 income, your LTD benefit is taxable at ordinary federal income tax rates. Use your marginal bracket to estimate the after-tax amount.

Example. A software engineer earns $180,000 per year in base salary. Her employer offers a 60% LTD benefit with a $12,000 monthly cap.

• Gross monthly LTD benefit: ($180,000 / 12) x 0.60 = $9,000
• The $9,000 is below the $12,000 cap, so the cap does not apply here.
• Her employer paid the premiums. She is in the 22% federal bracket. After-tax monthly benefit: $9,000 x (1 minus 0.22) = $7,020

Her essential expenses run $7,800 per month. Before adding Social Security Disability Insurance, her monthly gap is already $780.

Step 3: Account for the SSDI Offset and Approval Reality

Most employer LTD policies require you to apply for Social Security Disability Insurance benefits. They then reduce your LTD benefit by the SSDI amount dollar-for-dollar. This is called the SSDI offset clause.

The Social Security Administration approved only 21% of initial SSDI applications in fiscal year 2023. Approval timelines average 6 to 12 months. During that window, you receive no SSDI income at all.

Even after approval, the average SSDI monthly benefit was $1,537 as of January 2025. Higher earners receive more, but the program caps benefits. A worker with a strong earnings history might receive $2,800 to $3,200 per month.

Critical point. The SSDI offset means your total household income does not increase when SSDI is approved. Your LTD insurer simply reduces its payment by the same amount. SSDI approval benefits you only if your LTD policy has exhausted its maximum benefit period.

Factor SSDI into your gap calculation honestly. In most working years, it reduces your gap only if your policy has no offset clause, or after your LTD benefit period ends.

Step 4: Run the Full Gap Calculation

Apply the formula with real numbers.

Example 1: Mid-career professional, $180,000 base salary.

• Monthly essential expenses: $7,800
• After-tax LTD benefit: $7,020
• SSDI offset applies, no net SSDI gain during LTD period
• Monthly income gap: $7,800 minus $7,020 = $780 per month
• Over a 24-month disability: $18,720 shortfall

This gap looks manageable. But it assumes no reduction in investment contributions, no medical cost increases, and no delays in LTD approval.

Example 2: Senior executive, $300,000 base salary.

• Employer LTD policy: 60% benefit with $12,000 monthly cap
• Gross monthly LTD benefit: ($300,000 / 12) x 0.60 = $15,000, but capped at $12,000
• After-tax at 32% federal bracket: $12,000 x (1 minus 0.32) = $8,160
• Monthly essential expenses: $14,500 (mortgage, private school tuition, debt service, insurance)
• Monthly income gap: $14,500 minus $8,160 = $6,340 per month
• Over a 36-month disability: $228,240 shortfall

The $12,000 monthly cap is where high earners get hurt. The policy benefit percentage is irrelevant once the cap applies.

The Role of Supplemental Individual Disability Insurance

Individual disability insurance policies, purchased outside your employer's group plan, do not apply SSDI offset clauses in most cases. They also define disability more favorably, often using an "own-occupation" standard rather than the more restrictive "any-occupation" standard in group policies.

An individual policy that pays $4,000 per month closes the $6,340 gap in Example 2 by more than 60%. The remaining $2,340 gap is addressable through liquid reserves.

The IRS treats individual disability insurance benefits as tax-free income if you paid the premiums with after-tax dollars. That tax advantage amplifies the effective coverage relative to the gross benefit amount.

Use the CalcMoney Disability Income Gap Calculator

The four-step process above requires accurate inputs to produce a usable number. A single incorrect assumption, such as forgetting the monthly benefit cap or misidentifying the taxability of your policy, can understate your gap by tens of thousands of dollars.

The CalcMoney disability income gap calculator runs this math in real time. Enter your salary, your policy details, your benefit period, and your essential expenses. The tool outputs your monthly gap, your cumulative shortfall over one, three, and five-year disability scenarios, and the monthly individual policy benefit needed to close the gap.

That number is what you bring to an insurance agent. Not a general inquiry. A specific coverage target.

Calculate your exact disability income gap now →

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Results are estimates for informational purposes only. Consult a licensed financial professional before making financial decisions.