February 28 is not as far away as it feels right now. Most employers arrive at T4 season in January with messy records, missed remittances they did not know about, and employee information that has not been updated in months. October is the right window to fix all of that before it becomes a problem.
Match your remittances to your payroll records
Log into CRA My Business Account and compare what you remitted each month to your payroll totals for the same periods. They should match closely. Discrepancies are usually the result of a missed payment, a remittance sent under the wrong account number, or a pay run that was processed but never reconciled. Finding a gap now gives you time to resolve it quietly. Finding it in February, when it shows up on your T4 Summary, means a call to the CRA during their busiest season.
Confirm you have a TD1 on file for every employee
The CRA expects a completed federal and provincial TD1 on file for every active employee. If you hired someone this year and did not collect one at the time, follow up now. An employee without a TD1 should have been taxed at Claim Code 1 throughout the year. If a different claim code was applied without the paperwork to support it, correct it before you generate T4 slips. You do not send TD1s to the CRA, but you need them on file if you are ever audited.
Check on employees who left during the year
Every employee who stopped working for you this year, whether they quit, were laid off, or finished a seasonal contract, should already have a Record of Employment (ROE) on file. ROEs are due within 5 calendar days of the end of the pay period in which the employee last worked. Late ROEs are one of the more common compliance gaps the CRA catches. While you are at it, confirm the province of employment is correct for each person. It affects which provincial tax rates were applied all year and which province appears on their T4.
Spot-check your year-to-date deductions
Look at employees who had unusual pay periods this year: a retroactive raise, an unpaid leave, a one-time bonus, or a change in pay frequency. These situations can create small errors in CPP, EI, or income tax totals that are easy to miss mid-year and harder to explain at T4 time. If anything looks off, trace it now while the pay runs are recent enough to make sense of.
Update addresses and confirm SINs
T4 slips go out to the address you have on file. An employee who moved and did not tell you will not receive theirs, which delays their tax filing and creates extra work for you. This is also a good time to confirm every Social Insurance Number on file is correct. A T4 filed with a wrong SIN gets flagged by the CRA and requires an amendment to fix.
Set your year-end reminders now
Three dates to put in your calendar: December 31 to confirm all pay runs for the year are complete and reconciled, late January to generate and review your T4 slips before the deadline rush, and February 28 as the hard cutoff to file with the CRA and distribute copies to employees. If you have 6 or more employees, you are required to file electronically. The T4 Summary must be filed at the same time as the individual slips.
If you run payroll in PayCub, your T4 slips are populated automatically from your pay run data and the review step is quick. The goal of doing this audit in October is to make that review take 20 minutes in February instead of an afternoon.