Understanding military leave accrual and use-or-lose risk
Introduction to active-duty leave planning
Military leave normally accrues at 2.5 calendar days for each month of active service , or 30 days during a full year. A balance can continue growing while a member is deployed, on temporary duty, or using ordinary leave. Certain non-accruing statuses, including excess leave and some periods of unauthorized absence or confinement, require official accounting that this planning tool cannot reproduce.
The calculator estimates leave earned between two dates, adds the balance carried into the period, and subtracts chargeable leave already used. It then continues the projection to September 30, subtracts future leave you plan to take, and compares the result with the selected carryover cap. This makes the result more useful than a simple monthly accrual total: it shows both the likely balance and the number of days that may become use-or-lose.
Use the result alongside your Leave and Earnings Statement. The LES remains the official record because it includes transactions, corrections, protected special leave accrual, and duty-status details unavailable to a browser calculator. The estimate is best used early enough to reserve leave dates, discuss coverage with a supervisor, and avoid discovering a large at-risk balance late in September.
Compare a projected leave balance with the BF BAL, ERND, USED, and CR BAL fields on the applicable LES.
The formulas and official partial-month accrual bands
A full month earns 2.5 days, but a partial month should not be estimated by dividing 2.5 by an average number of calendar days. Service leave tables use half-day increments grouped into six-day bands. The calculator applies those bands separately to the entry month and final month, while every complete intervening month receives 2.5 days.
Partial-month military leave crediting bands
Day of month Credit when service starts Credit when the period ends
1–6 2.5 days 0.5 day 7–12 2.0 days 1.0 day 13–18 1.5 days 1.5 days 19–24 1.0 day 2.0 days 25–31 0.5 day 2.5 days
Let f (d ) represent leave credited through day d of a month. The ceiling function moves any served day within a six-day band to the corresponding half-day credit, while the minimum prevents a month from earning more than 2.5 days.
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For service from day a through day b in one calendar month, the month’s credit is f (b ) − f (a ) + 0.5. Adding each month produces earned leave E . The estimated balance L then uses the carried-in balance C and chargeable leave used U :
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The future projection calculates additional accrual from the as-of date through September 30 without crediting the current month twice. Planned leave is then subtracted. Enter all balances and usage in days; half-day values such as 12.5 are accepted.
September 30 balancing and the use-or-lose formulas
The federal fiscal year runs from October 1 through September 30. For most members, no more than 60 days may carry into the next fiscal year. An approved special leave accrual status may protect a higher balance, subject to current eligibility and expiration rules. Selecting a 90-day cap here changes the planning comparison only; it does not establish SLA eligibility or prove that excess days are protected in the pay system.
If B is the projected September 30 balance and K is the authorized cap, the amount at risk is the positive portion of B − K . The amount carried is the lower of the balance and the cap:
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A projected use-or-lose value is a scheduling signal, not a forecast that leave will definitely be forfeited. Taking additional chargeable leave before the cutoff reduces the projected balance one day for each day used. Approved SLA may change the applicable cap, while a finance correction or previously unposted leave transaction can change the starting figures.
Worked example: projecting a September 30 balance
Suppose a member begins January 1 with 5 days, uses 10 chargeable days, and checks the balance on September 30. Nine complete months earn 22.5 days. The estimated balance is 5 + 22.5 − 10, or 17.5 days . Because the as-of date is already September 30, there is no remaining accrual in that fiscal year. With a standard 60-day cap, the result is safely below the ceiling and the use-or-lose estimate is zero.
For a higher-balance example, assume a member starts the fiscal year with 58 days, has earned 14 days by mid-March, and has used 4 days. The current estimate is 68 days. If another 16 days will accrue before September 30 and 10 planned days will be used, the projected balance is 74 days. Against a 60-day cap, 14 days remain at risk. Planning those additional days in spring provides far more flexibility than waiting until the final weeks of September.
How to use the military leave projection
For normal fiscal-year planning, leave the start date at October 1 and enter the brought-forward balance shown on the first LES for that fiscal year. Set the as-of date to today or to the cutoff represented by the LES being reconciled. Enter chargeable leave used since the start date, excluding passes, permissive temporary duty, and other non-chargeable absences.
Next, enter leave that is already planned between the as-of date and September 30. Choose the standard 60-day cap unless an appropriate authority has approved and recorded SLA or another cap applies. A custom cap is available for unusual planning cases, but it should not be treated as authorization.
After calculating, review the earned leave, current balance, future accrual, projected September 30 balance, and use-or-lose estimate together. The chart shows where the estimated trajectory crosses the cap. The schedule can be copied or downloaded as CSV for a planning discussion. If separation or retirement is approaching, use the related military leave sell-back and terminal leave calculator . Federal civilian leave follows different rules and should be evaluated with the federal employee leave calculator .
Authority, assumptions, and limitations of this leave estimate
The statutory foundation is 10 U.S.C. 701 , which addresses leave entitlement and accumulation. DoD Instruction 1327.06 implements leave and liberty policy, while service publications provide detailed partial-month tables and administrative procedures. Rules for payment of unused leave appear in 37 U.S.C. 501 . Sources and policies should be checked again when an official decision depends on the result.
The model assumes continuous leave-earning service throughout the selected dates.
Past leave is entered as one total, so historical monthly rows do not reproduce the exact posting date of every transaction.
Planned leave is spread across remaining months for charting; the final projected balance is based on the full entered total.
SLA days are not aged individually, and their expiration dates are not modeled.
Drilling Guard and Reserve service is not continuous active duty; separate active-duty periods may need separate calculations.
The LES and the servicing finance office remain authoritative.
Military leave accrual frequently asked questions
How fast does military leave accrue?
Active-duty members generally earn 2.5 calendar days for each month of active service, totaling 30 days in a full year. Accrual can continue while ordinary leave is being used, but certain non-accruing statuses require official review.
How much leave is earned in a partial month?
Partial months use half-day crediting bands rather than an average daily rate. Service through days 1–6 earns 0.5 day, 7–12 earns 1.0 day, 13–18 earns 1.5 days, 19–24 earns 2.0 days, and day 25 or later earns 2.5 days.
When does use-or-lose leave disappear?
Ordinary days above the authorized carryover cap are generally subject to fiscal-year balancing after September 30. Members should verify the LES and any SLA protection rather than relying only on a projected number.
Why might the LES differ from this estimate?
The LES can include non-chargeable absences, delayed transactions, audit corrections, non-accruing statuses, restored leave, and separately protected SLA days. Reconcile the calculator’s starting balance, earned amount, and usage total with the corresponding LES fields.