It’s always best to set more than one goal to avoid disappointment if some unfavourable conditions (like bad weather, or coming down with flu) disrupt your plans on marathon day.
Instead of setting a single time target, it’s wise to widen your goals so that you’ll increase your chances of success. Choose a time window for your finish (for example, 4:00 to 4:15); it’s psychologically much better than pinning all your hopes on one magical time.
Always set practical goals that won’t overextend you in the race could be: start slow and then increase your pace; or perhaps hold an even tempo the entire race, or maybe simply finish without injury.
The choice of your goals depends on being confident that your training performance will let you achieve them.
Make goals at, enable, and your experience will be positive, and you’ll approach the race with more confidence.

[Photo: Visualphotos.com]
If you do want to attempt a specific time goal, here’s a rough guide, based on current race form. If you haven’t been running recently, simply focus on finishing your first marathon feeling comfortable.
10K | Half-Marathon | Target |
60 mins+ | 2hrs 11+ | 5hrs+ |
51-59 mins | 1hr 55 – 2hr10 | Sub- 4hrs 30 |
44-50 mins | 1hr 40 – 1hr 54 | Sub- 4hrs |
38-43 mins | 1hr 25 -1hr 39 | Sub- 3hrs 30 |
Under 38 mins | Under 1hr 25 | Sub- 3hrs |
Marathon Pace Calculator: https://www.active.com/fitness/calculators/pace