A double booking just happened. Here is how to find out why, and stop the next one

Open both clashing entries side by side before you change anything. Moving or deleting one of them first destroys the evidence. Then work through these questions in order. Most clashes are explained by the first three.

Question 1: Which calendar held the clashing event?

Look at the entry that was already there when the booking came in. Note the account (Google or Microsoft), the calendar name and the colour. Then check your booking tool's connected calendars list. If that calendar is not on the list of calendars checked for conflicts, you have found the cause. This is the most common one, especially with second Google calendars ('Family', 'Clinic', 'Site visits'), a work Outlook account added after you set up, or a calendar someone else shared with you.

Fix: connect the account if it is not connected, then tick that specific calendar for conflict checking. Calenix connects Google Calendar and Microsoft Outlook. The Free plan includes one connected calendar and the Individual plan up to six, so if you have run out of connections, either upgrade or consolidate commitments into a calendar that is already checked. Our guides to syncing your booking calendar with Google Calendar and connecting Outlook to your booking page walk through the settings.

Question 2: Was the event marked busy?

Open the clashing event and look at its availability setting. In Google Calendar it shows as Busy or Free. In Outlook it is 'Show as' with Free, Working elsewhere, Tentative, Busy or Away. Conflict checks generally read free/busy status, so an event marked Free is treated as open time. Invitations you accepted from other people, webinars and reminders you set up years ago are frequent culprits, as are tentative replies.

Fix: change the event to Busy. If it repeats, change the whole series, not just this occurrence. Decide once how you treat tentative holds and apply it consistently.

Question 3: Was it an all-day event?

All-day entries are often created as Free by default, because people use them for notes such as 'Mum's birthday' or 'Invoice day'. If you used one to mark leave, a conference or a site day, it may not have blocked anything.

Fix: set all-day entries that mean 'unavailable' to Busy, or replace them with a timed event covering your working hours.

Question 4: Was it private, delegated or on someone else's calendar?

Private events normally still count as busy for free/busy purposes; the title is hidden, not the time. Problems start with delegated and shared calendars. If an assistant or colleague adds an appointment to a shared team calendar, or to your calendar through delegate access in a way that lands on a calendar you have not connected, your booking page never sees it.

Fix: agree which calendar delegates must write to, and make sure that calendar is checked for conflicts. If a shared calendar holds many people's events, do not connect it as your conflict calendar, or everyone else's appointments will block your time. Ask for your entries to be added to your own calendar instead.

Question 5: Do the times match once time zones are applied?

Compare the start times in both systems. A one-hour difference is the giveaway. Common sources are a booking tool set to the wrong home time zone, an event created while travelling, a calendar whose own time zone setting differs from your device, and daylight saving changes in the UK (late March and late October) or in parts of Australia (early October and early April). Our guide to scheduling meetings across time zones covers the offsets.

Fix: set your time zone by city in Calenix and in each calendar, and check events created during travel.

Question 6: When was each entry created?

Check the creation or invitation time on both. If the personal event was added only a minute or two before the client booked, or two people booked the same slot almost at once, you are looking at a timing gap: calendar changes do not always reach a booking tool instantly.

Fix: add personal commitments as early as you can, and avoid making last-minute changes to your diary during busy booking periods. If this cause repeats often, it is worth asking support how quickly your connected calendars refresh.

Question 7: Did the booking come through the booking page?

If one of the two appointments was typed straight into a calendar after a phone call, a text or a chat at the door, and the other came through the booking page, the question is which arrived second. A booking tool cannot block a time that was only promised verbally, or written in a paper diary or an unconnected calendar.

Fix: make the booking page the route for every booking, including the ones you take by phone. You can open your own page and book on the client's behalf.

Bonus: the calendar you cannot connect

Apple iCloud Calendar is not a Calenix integration. If a clash came from an iCloud calendar, either move those commitments into Google or Outlook and view them on your iPhone, or copy key dates across as busy blocks. Our page on Apple Calendar and online appointment scheduling explains the workaround.

Each double booking costs more than the slot. Someone is told their appointment has moved, a client sits in a waiting room, or you join a call ten minutes late from another meeting. Clients forgive one clash. A second one, especially for the same client, starts to look like disorganisation.

Fixing the immediate clash without finding the cause means you are relying on luck. Most causes are structural: a calendar not connected, a habit of accepting invitations as free, or a staff member who writes in the wrong calendar. They do not go away on their own, and they tend to get worse as you add calendars, staff or clients in other time zones.

A short, repeatable diagnosis also changes how a team talks about mistakes. Instead of 'who booked over me?', the question becomes 'which of the seven causes was it?'. That keeps the conversation on the system, not the person, and the fix usually takes less than five minutes once you know where to look.

Finally, the record of causes is useful in itself. If three of your last four clashes came from one shared calendar or one booking channel, that tells you where to put effort. If you run both a Google and an Outlook diary, our guide on scheduling across Google Calendar and Outlook is a good next read.

A fictional two-osteopath practice in Cambridge takes most bookings online for 45-minute treatments. Each osteopath has a booking page on Calenix. In early October 2026 they had two clashes in a week and ran the diagnosis on both.

Clash 1: Tuesday 13 October, 10:30

A new patient booked online at 10:30, but the osteopath was already on a home visit. The home visit had been added by the part-time receptionist to a shared Google calendar called 'Practice visits'. That calendar was visible on everyone's phone but was not connected for conflict checking. Cause: calendar not connected. Fix: rather than connect the shared calendar, which would have blocked both osteopaths for every visit, they agreed the receptionist would add each visit to the treating osteopath's own Google Calendar, which was already checked.

Clash 2: Thursday 15 October, 14:00

A follow-up patient booked into a slot during an online CPD session. The CPD invitation had arrived in the osteopath's Outlook account and had been accepted as Tentative. Outlook was connected, but tentative events were not blocking time. Cause: event status. Fix: change the series to Busy and adopt a simple rule: anything you intend to attend is Busy.

The second osteopath also had a personal Google calendar and an Outlook account from teaching work, so she needed three connected calendars. That took her beyond the Free plan's single connection, so she moved to the Individual plan, which allows up to six.

The illustrative maths: if each clash costs one 45-minute treatment at £55 because a patient has to be rebooked or does not return, two clashes a month is £110, or £1,320 a year, before counting the time spent apologising. A ten-minute monthly check is a cheap way to protect that.