Microsoft offers the Office productivity suite either as a one-time purchase for the traditional, standalone collection of desktop tools or through an Office 365 subscription. While both options are on the table, Microsoft has not been all that subtle when it comes to which model it thinks users should embrace. Now, with the launch of Office for iPad, the Office 365 subscription wins hands down.

Some users balk at the idea of paying for Microsoft Office indefinitely. The fact is that Office 365 is less expensive up front, possibly less expensive over time, and includes a variety of perks and benefits that you don’t get with the standalone suite — like Office for iPad.

When you buy the standalone Microsoft Office desktop suite, that’s all you get. The desktop suite costs significantly more up front and is licensed for only one PC. Period. Office Home & Student 2013 costs $140, and it only includes Word, Excel, PowerPoint, and OneNote. For $220, you can get Office Home & Business 2013, which adds Outlook — or for $400 you can get Office Professional 2013, which includes everything in Office Home & Business 2013, plus Publisher, Access, and some additional tools.

Compare that to Office 365. Office 365 Personalcosts $70 per year. It includes licensing for the current version of Office on a PC or Mac, and on a tablet, and it also comes with 20 GB of cloud storage on OneDrive, plus 60 minutes per month for Skype calls. Just comparing the value of Office 365 Personal against the cost of Office Professional 2013, it will take almost six years of Office 365 subscription payments before you’ll spend the same $400.

By that time, Microsoft will most likely have launched one, possibly two new versions of the productivity suite. Office Professional 2013 and the $400 investment will be obsolete in a couple years, but the Office 365 subscription includes the most current version of Office, so you’ll always have the most up-to-date tools. Even if you don’t really need all of the applications in Office Professional 2013, it would take two years of Office 365 Personal to equal the $140 that it would cost to buy Office Home & Student 2013, and you wouldn’t get the additional benefits.

For a family, the math is even more compelling. For $100 a year, the Office 365 Home subscriptionprovides licensing for up to five individuals to install the current version of Office on a PC or Mac, as well as on a tablet, and each person also gains the additional Skype calling minutes and OneDrive storage space. Purchasing five copies of the standalone Office Professional 2013 suite would cost $2,000, so it will take 20 years of subscribing to Office 365 Home before it hits a break even, and that doesn’t include the extra perks that come with Office 365.

As far as I’m concerned, the math has always favored Office 365. There has been some confusion from customers under the impression that Office 365 is a cloud-based version of Office, but the reality is that you’re buying the exact same software — you’re just paying for it a different way, and getting a variety of benefits in exchange.

Office for iPad is icing on the cake. The Office for iPad apps are very well designed and essentially bring the full power and features of the Office desktop suite to the Apple tablet. Microsoft has done a superb job customizing the Office experience for a touch screen environment, and we can expect that similar touch-enabled apps will soon come to Windows 8 / RT and Android. To unlock the full value and productivity of the tablet-based Office apps, you must have an Office 365 subscription.

For what it’s worth, you don’t have to buy Microsoft Office at all — neither the desktop suite nor the Office 365 subscription. If you’re okay relying on web-based tools, you can use Office Web Apps for free through Microsoft’s OneDrive site. They don’t have all of the features and functions of the full Microsoft Office programs, but they’ll get the job done.

You can also use free tools that are roughly equivalent to Office like Google Docs, Apple’s iWork programs (Pages, Numbers, and Keynote), or a free open-source suite (including LibreOffice). All of these alternatives are good enough for most cases. However, if you have to work frequently with Microsoft Office file formats, you’re better off with the real thing, because other productivity tools frequently mess up the formatting when working with Office file formats.

Ultimately, if you’re going to buy Microsoft Office, make sure you do yourself a favor and sign up for Office 365 instead of just buying the Microsoft Office desktop suite.

Is Office 365 the best office suite for your business needs? Share your thoughts in the discussion thread below.