If you are using TurboBASIC, PDS Basic, GW-BASIC, QuickBasic, or PB/DOS there is no easier path to Windows than PowerBASIC!
Your functional code (conditions, assignments, file handling, etc.) will port over with little to no change, depending on what BASIC you are converting from. Code dealing with devices and user interaction will need to be rethought and re-written because DOS and Windows are two different operating systems. You'll need to make changes to your code to give your program the look and feel of Windows.
How much work is it to convert my DOS-based programs to Windows?
A large part of this answer depends on the complexity of the program and the skill of the programmer that does the conversion. While we can't estimate the "work", we can explain the things that must be done by the programmer.
We make two compilers for Windows - PowerBASIC for Windows (PB/Win) and PowerBASIC Console Compiler (PB/CC). Each one has its own requirements that your DOS-based source code must meet.
PowerBASIC for Windows
This is the crown jewel to aim for. PowerBASIC for Windows let's you create applications with that look and feel Windows applications have. Your program will have buttons, menus, scroll bars - all the elements you see in modern professional applications! These are not in your DOS-based programs, so clearly you'll need to write the source code that enables them. Under Windows you do not have direct control of devices, and interaction with the user must be done the way Windows wants you to do it. For example, when running a Windows application you'll notice there is no prompt line. User input is done by presenting a dialog window with edit fields in it, typically with an OK and Cancel button. This means that any DOS code like LINE INPUT is not going to work. You will need to create a dialog window with the edit fields and buttons and statements to tell your program how to respond to them. (See PowerBASIC Forms - it's a great tool for creating user interfaces).
PowerBASIC Console Compiler
With our other compiler for Windows, the PowerBASIC Console Compiler, you create true 32-bit Windows applications that run in the console window (some say "DOS box"). These text-only programs look and feel like DOS applications but run with 32-bit speed - and you have access to gigabytes of memory!
Conversion from DOS-based BASIC to PB/CC is much easier than to PB/Win. You'll need to make some changes but you won't need to rewrite your interface. The PB/CC manual is on-line (https://www.powerbasic.com/support/help/pbcc/). In the Programming Reference section is a topic "Upgrading to PBCC" which spells out the differences between DOS and Windows BASIC.
Lots of our customers have done these conversions. Many of them are members of our web site-based Forums. The PowerBASIC Peer Support Forums consist of over 200,000 searchable posts!
In summary, while no product can simply recompile your DOS source code and produce Windows applications, there is no easier path to Windows than PowerBASIC!