When there is confusion in a system because of the excess of variables or its possible distortion, it’s advisable to try to look closer at the origins of the problem trying to find more clarity. From this comes the concept of personal inflation (PI).

Although all the parts of the economy are interrelated, they don’t have a prefect correlation. Thus, if you can estimate the inflation data that directly affects the retired person, precision will be enormously improved.
Most likely, the price increase in university education isn’t a relevant factor for someone that isn’t going to start their studies, in the same way that the increase in housing prices isn’t to those who already own their own house and who intend to leave it to their inheritors.

A borderline case happens with **health costs**. For some, not being included in any type of public protection system is nearly their greatest worry, while for others it’s contemptible to find themselves under the state’s umbrella.
Therefore, as a first step, it would be necessary to calculate those areas that can affect retirement and obtain specific historical data. As an example, you can imagine a couple that decides to
retire to the Philippines. They rent, don’t have a car and have global health insurance. This couple will need to know the details of their last few years of rent in the Philippines and the evolution of health insurance in a global way. The rest of their expenses such as: food, telephone, Internet, electric, and water; affects them to a lesser extent and the average could be used to calculate them.

If they estimate a monthly payment of $500 on rent, $400 on insurance, and $800 on the rest of their expenses, and on average in the last few years rent has risen 8% annually, health insurance 7% and the country’s inflation is 2%, the following calculation can be made to obtain the personal inflation data:

PI=(500x8%+400x7%+800x2%)/(500+400+800)=4.9%

Calculating future monthly expenses isn’t complicated; in fact, it is where less uncertainty appears, despite the fact that uncertainty is always found in the future. What is not as trivial is estimating an average inflation for the retirement period. Perhaps rent in Manila has risen a lot in the last few years, but you encounter an unsustainable situation and it’s nothing more than the reflection of a real estate bubble that is on the brink of bursting. Or maybe the historical data on housing rentals in the last 30 years didn’t take the current situation into account. The solution to this problem doesn’t exist. Once again, you can make a reasonable approximation. If we call the average increase in rent in Manila in the last 30 years IA30, 3%, and IA5 the average increase in the last 5 years, 10%, as an example the following could be used:

i . If the couple is young, you can give more weight to the historical data, IA=(2xIA30+IA5)/3=5.3%.

ii . If the couple is old, then the recent data is overvalued, assuming that they have fewer years to live and there won’t be time for inflation to return to the average, IA=(IA30+1.5xIA5)/2.5=7.2%.

iii . The age of the couple is omitted and you simply use 1.5 times the official inflation of the rent history, IA=1.5xIA30=4.5% (you don’t use double, as in the general case seen previously, as in specific areas the distortion between the actual inflation and the official is less).

Logically, this is only an example. The weight of each type of inflation varies according to the particular scenario of the person making the calculations. In any case, prudence requires leaning towards a high inflation figure as a more restrictive situation.
Therefore, it’s possible to calculate personal inflation without knowing more than the areas of expenditure that each one has and finding average inflations specific to each. Estimating these average inflations is an art, which can be used for future inflation. This applies as much to the historical data exclusively multiplied by a coefficient of security (for example 1.5), as to a combination of these historical figures with the more recent ones.

**DYNAMIC MODEL**

It’s healthy to make an estimation about future inflation through the methodology that is considered appropriate. However, to remain only with the initial calculation and never make a periodic follow-up during the retirement years would be a shame. This will be a constant in all the variables that affect retirement.

Recalculating the estimated future inflation each year or every other year upon retirement diminishes carrying forward previous errors and permits correcting the rhythm of expenses (or possible extraordinary income) to the new situation of corrected inflation. It is, therefore, a dynamic model, a process that doesn’t end during the whole of retirement.