How PTO Accrual Works: Projecting Your Vacation Balance Month by Month

June 18, 2026 7 min read HRPTOleaveaccrual

"How much vacation will I have by August?" is one of the most common questions an employee asks and one of the hardest to answer by guessing. The number in your HR portal today is a snapshot, not a forecast — it tells you what you have earned so far, not what you will have earned by the date you actually want to take off. The good news is that paid time off almost never appears in a single lump on a mystery date. It accrues: it builds at a steady, predictable rate, and once you know that rate you can project your balance forward to any future month with simple arithmetic.

Accrual means earning leave as you work

Under an accrual model, your annual vacation entitlement is not handed to you on day one. Instead, you earn a fraction of it for each unit of time you work — each pay period, each month, or in some systems each hour on the clock. By the end of the year you have accumulated the full annual figure, but at any moment in between you hold only the portion you have earned to that point. This is the opposite of a front-loaded or "lump-sum" policy, where the entire year's allowance lands in your balance on a fixed date (often January 1st or your work anniversary) and you draw it down from there.

The reason accrual is so widespread is that it ties the benefit to time actually served. Someone who leaves in March has earned roughly a quarter of the year's leave rather than the whole thing, and someone who joins mid-year starts building a balance from their start date rather than waiting until the next annual reset. It is fairer to both sides, and it is the model the Vacation Accrual Projector is built around.

The accrual rate is the whole game

Everything about a forecast comes down to one number: how much leave you earn per period. To find it, you divide the annual entitlement by the number of accrual periods in the year. The math is the same whichever frequency your employer uses:

Monthly — 15 days a year ÷ 12 months is 1.25 days per month. This is the cleanest unit to think in, and it is the basis the projector uses to show your balance building month by month.
Semi-monthly — paid on the 15th and the last day, that is 24 periods, so 15 days ÷ 24 is 0.625 days per paycheck.
Bi-weekly — 26 pay periods a year, so 15 days ÷ 26 is roughly 0.577 days per paycheck.
Hourly — common for part-time and shift work: 15 days at 8 hours each is 120 hours, spread across roughly 2,080 full-time hours a year, or about 0.0577 hours of leave per hour worked.

These all converge on the same annual total — they just slice it differently. The headline "15 days a year" is the same benefit whether it lands in twelve monthly chunks or twenty-six payroll chunks; only the granularity of the steps changes.

Projecting the balance month by month

Once you have the monthly rate, projecting forward is straight-line addition. Starting from your reference date, you add the per-month accrual for each month that passes: after one month you hold 1.25 days, after two months 2.5, after six months 7.5, and after a full twelve months the complete 15. Plotting that progression is exactly what turns a vague "sometime in the summer" into a concrete "I will have crossed ten days by the start of September."

This is where most by-hand estimates go wrong. People tend to either assume they already have their full annual allowance available (they don't, unless the policy is front-loaded) or forget to count the months still to come before the trip. The straight-line projection removes both errors: you give it a start date and an annual figure, and it lays out the accumulated balance for each of the next twelve months so you can read off the month your balance will finally cover the leave you want to book.

The caps and rules that bend the straight line

Pure accrual is a clean line, but real policies add ceilings and resets that the line eventually runs into. It pays to know which of these your employer applies before you rely on a projection:

Accrual caps. Many employers cap the maximum balance you can hold — often expressed as a multiple of the annual rate, such as 1.5× or 2×. Once you hit the cap, you stop accruing until you take leave and drop back below it. If you never use your time off, the straight line flattens out rather than climbing forever.
"Use it or lose it" and carryover limits. Some policies zero out unused leave at year end; others let you carry over a capped number of days into the new year. A few jurisdictions restrict or prohibit forfeiture of earned vacation entirely — California, for instance, treats accrued vacation as earned wages that cannot simply be taken away — so the rule that applies to you depends heavily on where you work.
Waiting periods. New hires are sometimes barred from using accrued leave during an initial probationary period, even though the balance is quietly building the whole time.
Negative balances. Some employers let you borrow against future accrual and take leave before you have technically earned it, leaving you with a negative balance that the next months' accrual pays back.
Tenure tiers. Many policies raise the accrual rate after a few years of service — 15 days a year might become 20 at the five-year mark. The line does not just continue; it gets steeper on your anniversary, so a projection that runs past a tier boundary understates the back half unless you account for the step up.

None of these change the underlying rate; they change what happens at the edges. A projection gives you the unobstructed accrual curve, and knowing your policy's caps and resets tells you where that curve gets clipped.

The lag cuts both ways when you leave

Accrual does not only govern what you can book — it governs what you own. In many places the unused leave you have accrued is paid out when you resign, which makes your balance on your last day a real number on your final payslip rather than a perk you forfeited. The symmetry is the part people miss: leave you have taken but not yet earned can often be clawed back from that same final pay.

That is the practical sting of the gap between your annual entitlement and your accrued balance. Take three weeks in February against a 20-day annual figure, resign in the spring, and you may have used roughly twice what you had actually accrued by then — and owe the difference back. Knowing your accrued balance on any given date is not just about whether a holiday request clears; it is about understanding what you actually hold at that moment, in either direction. The same month-by-month projection answers both questions.

Planning a trip around the numbers

The practical payoff is being able to plan backwards from the leave you want. If a trip will cost you ten working days and you are accruing 1.25 a month, you can see precisely how many months of accrual stand between your current balance and that ten-day requirement — and therefore the earliest month you can take the trip without going into the red. That turns "can I afford this holiday yet?" from an anxious guess into a date you can point to, and it lets you stagger requests so you are not constantly bumping against a zero balance or an accrual cap.

It also helps at the other end of the curve. If you are approaching a cap or a year-end forfeiture date with a large balance, the projection shows you how soon you need to book time off to avoid leaving earned days on the table. Either way, the decision rests on the same straight-line math.

Project your balance, then plan

The whole forecast comes down to two inputs: when you are counting from, and how many days a year you earn. The Vacation Accrual Projector takes your start date and your annual entitlement and lays out the accumulated balance for each of the next twelve months, so you can read off exactly when you will have enough banked for the leave you have in mind. Enter your real annual figure, find the month your balance clears the trip you want, and book around it rather than guessing.

General information, not legal or HR advice. Accrual rates, caps, carryover limits, waiting periods and forfeiture rules vary by employer and jurisdiction and change over time — confirm your actual entitlement and balance against your own policy and local law before relying on a projection.