Can my HST registration be backdated if I forgot to register on time?

Yes, the CRA can backdate your HST registration to the date you were first required to register. This matters because you remain legally obligated to remit HST on taxable supplies you made after that required registration date, whether or not you collected it from customers. If you did not collect HST during that period, you generally must still remit it out of your own pocket.

The CRA may also assess penalties and interest on late registration and on any HST that should have been remitted but was not. However, the CRA's Voluntary Disclosures Program (VDP) may still be available even if the CRA has already made some contact with you about the issue — coming forward before any contact gets the most relief, but a "prompted" application after limited contact can still reduce penalties, though interest relief is more limited.

Retroactive registration does have one upside: you may also be able to claim input tax credits for HST you paid on business expenses during that missed period, subject to time limits. Given the financial exposure, it is worth getting advice from a tax professional before approaching the CRA about a backdated registration.