Why the litter station makes the calendar work
Litter cleaning is the one cat chore nobody can postpone for long, so a calendar hung there gets looked at daily by whoever does the cleaning. That built-in audience is the whole point: a due date written beside the tray is seen by the person scooping, the person feeding, and anyone covering for them, without anyone opening an app or remembering a system.
Hang the calendar at standing eye height, not down at tray level, and keep a pen on a string or in a pot right beside it. A calendar you cannot write on in the moment becomes decoration; the pen is what turns a glance into an updated record.
Marking due dates so they stand out on the page
Write the vaccination due date across its square in thick pen, with the cat's name and what is due — not just a cross or a dot, which future-you will not decode. A few weeks earlier, draw a ring around the booking date and write the clinic's name inside it. Those two marks, in the same ink every time, become a pattern your eye learns to spot while you clean.
If two cats share the litter station, give each cat a different pen colour and keep both pens by the calendar. Write the cat's name on every entry regardless of colour, because colours fade, pens get borrowed, and a name never becomes ambiguous.
Turning daily cleaning into a quiet checking routine
Once a week, while the tray is being done, read ahead on the calendar to the end of the following month. Anything ringed in that window gets booked that week. This short forward scan is the routine that makes a paper calendar reliable: the due dates are passive, but the weekly scan is active, and it happens in a place you already stand every day.
When a vaccination is done, cross through the old due date with a single line — still readable — and write the new one in its future square straight away, ideally the same evening, from the certificate. The crossed-out history building up on old pages shows the rhythm of boosters at a glance when you flip back.
What the wall calendar cannot do, and covering for it
Paper by a litter tray lives in a humid, dusty corner and pages tear. Photograph each month page when you turn it, so a lost or damaged calendar does not take the year's dates with it. Keep the actual certificates elsewhere, in a dry folder — the calendar carries dates, not proof, and a cattery or new vet will ask for proof.
At the end of the year, copy any due dates that fall in the early months of the next calendar before the old one comes down, and check them against the certificates as you copy.
If the litter station is shared with a dog's feeding area or a busy back door, protect the calendar's visibility anyway: hang it on the wall face you look at while you work, not the one behind the door when it opens. A calendar that disappears behind an open door for most of the day loses the daily audience that makes this whole method function.
The wall calendar handles the daily reminding, while KinsLe's Pet Passport holds this cat's vaccination dates in one portable packet with the rest of the records, ready for any appointment or stay away from home.