Your VAT payment is due a set period after the end of each VAT return period, and the same deadline normally applies to filing the return itself. For most businesses that means one deadline per quarter. The definitive dates for your business are shown in your VAT online account, and that is what to work from.
Your specific dates depend on your VAT stagger — the quarterly cycle you were allocated at registration — or on monthly or annual filing if you use those. A business on a different stagger to yours will have entirely different deadlines, so a date you have heard from another business is no guide at all.
Some arrangements shift the timing. Direct debit collections are taken a few working days after the filing deadline. The annual accounting scheme replaces quarterly payments with instalments and a balancing payment. Businesses whose VAT liability is above a set size make payments on account during the quarter instead of a single payment at the end. Payment must also clear by the deadline, so allow for the clearing time of your chosen payment method.
Missing a deadline now feeds into a points-based penalty system: each late return earns a point, and a penalty becomes payable once you reach the threshold for your filing frequency. Late payment penalties and interest are charged separately, and both build the longer the liability is outstanding. The thresholds, penalty amounts and interest rates are published on gov.uk.
If you can see a VAT bill coming that you will struggle to meet, deal with it before the due date. Contact HMRC about Time to Pay, or look at whether a VAT facility is available to spread it. Availability and terms depend on the lender and your circumstances, and nothing is guaranteed.
This is general information, not tax advice. Confirm your own position with your accountant or HMRC.