Of course you can save a little time and math by looking on the Jepps for the parenthetical number next to MDA, which of course is the AGL and divide it by 300 to give you the VDP. All this is based on the standard 3 deg. GS.
This may be commons sense, but if you are able to use DME on any approach whether it is an on-field or off-field navaid, convert your VDP into DME. Then you simply wait for the DME that you calculated to arrive. After that point, its missed approach time or circle-to-land time.
If there is no DME to use on the approach then 10% of your MDH gives you the time to go to MAP. In other words, if you have an MDH of 500 ft AGL, then 50 seconds prior to the MAP is your VDP. Always try to use the count-down method.
If you know you need to circle to land prior to starting the approach, you are flying to higher minimums that allow such a maneuver. If you break out and are not in a position to land on the intended runway at straight in minimums, then you go missed approach. Thats why its called a "missed approach point", not a "this is the last instance you can land point".