lisa
If you are invoicing monthly never invoice on the first of the month, unless vat return is due.
1. Some companies have a policy of payment terms being 30 days from end of month, this means that if you invoice on the 1st of march, for instance, then the payment will only be due 30 days from the end of march, however should the company use these terms and you invoice on the 28th of February then the payment would be due 30 days from the end of February,
2. if your current 3 month vat return should run for arguments sake, from jan 1st to march 31st and you have invoices to send out at the end of march then depending on cash flow you can wait to send the march invoices out untill the first of april, hence the vat element of the work done in march would not fall due until the end of july, as your vat return from jan to march will not fall due till the end of april (no later),
3, the exception to the vat rule is when you ae using the cash accounting scheme, when vat will be due only on the invoices you have recieved payment on in the current vat period.
4, if you are using a program such as sage, this has the facility to amend the date on an invoice so if you are sending out on the 1st of feb it can be amended to the 29th of jan or can be amended from the 28th of the month to the 1st of the next month this can only be done when first typing the invoice and not once you have posted it to your accounts ledger, this is good for customers that want your services but have to alter dates on invoices either back or forwards to coincide with their bugets and monthly dept spend
hope this helps
regards
Solar