Now that you know how to plan for a specific goal, it's time to revisit an old concept so that you can set a target corpus.

The key to set a realistic target corpus is to predict what would be the value of the commodity when the corpus is ready. You can calculate that using some assumption of the inflation. One way to do that is to use past inflation data and project how the value might be in the future.

The biggest problem is that there is no common inflation across all categories. The inflation in real estate would not be the same as the inflation in grocery items. It may so happen that the town where you want to buy a property sees an improved economic activity in the future. This, in addition to the devaluation of currency might lead to a larger inflation in real estate prices. On the other hand, the inflation in grocery items might only be affected by the devaluation in currency. (Actually, the cost of living in an area, which is proportional to economic activity, also impacts cost of grocery items. Look at Britannia's biscuits. MRP of Cracker biscuits distributed in Bengal is about two-third of the MRP of the same commodity distributed in Karnataka.)

Still, it is possible to collect some form of local data. Use whatever you can get your hands on—government gazetted, discount advertisements, your old budgets, anecdotes—to arrive at a reasonable estimate of the inflation rate. Use the variation as a good indicator of how much margin of safety you should add so that you err on the side of caution. As a general thumb-rule, you should always add 10-15% to your target corpus and plan accordingly. For some commodities that fluctuate more, feel free to add more margin of safety.

Now revisit the investment plan and calculate your yearly, and subsequently your monthly contribution towards that goal.

Calculate monthly contribution and add a specific save-bucket against the plan.

The computation we have been doing so far focuses on a goal with a target date. While this is great for singular events in your life, it is ill-suited for goals that require systematic income—say, your retirement.