· AI HR Bot · 3 min read
Vacation accrual calculator — monthly, to the fourth decimal
Enter a policy and two dates; the calculator does the rest. It is the same arithmetic our Slack HR assistant runs when someone asks how many vacation days they have — a monthly accrual, held to four decimal places and reported to two, rounded down.
1.66 days/month
- Months completed
- 12
- Held on the books
- 20.0004 days
- What the bot reports
- 20 days
Assumes the policy has been active since the hire date and nothing has been spent. Balances are stored to four decimal places; the bot reports two, rounded down — it never states more days than are actually held.
The three rules it applies
A month completes on the monthiversary of the hire date. Someone hired on the 15th finishes a month of service on the next 15th; someone hired on the 31st finishes February on the 28th, because the count is clamped to the end of a shorter month — the clamp borrows the day, and the anniversary does not move.
The monthly rate is the annual figure divided by twelve and stored to four decimal places, which is why 20 days a year becomes 1.6667 a month and twelve months of it come to 20.0004 on the books — four ten-thousandths more than the policy says, an error the storage precision makes visible instead of hiding.
The reported figure is the stored one cut down to two decimals — rounded down, never up, so the number quoted is never more days than are actually held. Hold 10.99 and hear "11", and you would book a day you do not have; that is the direction the rounding refuses.
What it assumes, out loud
The calculator answers a deliberately simple question: what does a policy that has existed as long as the hire date hold today, if nothing has been spent? Real histories are messier, and the differences all run through your HR Head, whose guide covers setting the actual policy.
The product itself also anchors accrual at the later of the hire date and the moment the policy was created — nobody is credited for service predating the policy, and the bot does not owe anyone days from before it existed. The calculator skips that anchor on purpose, because it does not know your policy's birthday; when the two disagree, the bot's lower number is the true one.
Where the number lives day to day
If your team is in Slack, this arithmetic is a question, not a spreadsheet: asking the bot is covered in how to track PTO in Slack, filing what the number pays for is Leave Requests, and the full walkthrough of the accrual — watermarks, missing hire dates, switching it off — is in how a Leave Balance accrues.
Connects to your Slack in about 2 minutes.