We retired in 1989 at age 53. A 35 year timeline, to age 88. We're about 80% there.
Rather than looking at the past 25 years on the basis of how prices have risen, our view has been to maintaining our net worth with a lifestyle that is comfortable. Until age 70, we did everything we wanted to do, spent what we wanted to spend. Travel, entertainment and indulging in hobbies were all suited to our lifestyle. Without analyzing the costs in dollars or percents, our net worth has remained the same since 1989.
Since age 75, our expenses have slowly gone down. Again, not looking at the dollars, we simply don't spend as much. Travel almost nil, which means we can keep our older cars, but with virtually no operating and maintenance cost. We go out to eat much less often, and even our food bill has slowed, as we eat less and healthier. Clothing costs are essentially zero.
When the question comes up: "What have you bought recently?" ... we're hard pressed to think of any major purchases. No new decor, new appliances, or any kind of housing upgrade. Buying a newer CCRC designed home put us in a position where upgrades, repairs, or any major expenses have not been necessary.
Medical costs after age 65, when we went on to Medicare... are a known factor.. a roughly $10K figure that has not materially changed.
So... as to inflation... Basically, the effect of inflation will only be on our costs of food, utilities, base housing taxes.
Our investment dollars are in semi safe long term inflation adjusted I bonds.
Enough... Re: the OP:
This leads me to wonder if we overestimate inflation in retirement, or if perhaps the CPI itself overstated as it affects us, and if we underestimate our own ability to deal with increasing prices. This is not an argument to increase the withdrawal rate, but it does raise the question of just how much portfolio risk do we need to take.
I would say that this has been our situation. Real life often supercedes mathematics. In our case, money has not been a major concern. The real life changes in what we do, have just normally seen a reduction in expense.
Perhaps we just slipped in to old age "stuff" early. Most of our members seem to believe they will not slow down, and have plans for travel and social activities well into their 80's and 90's. Planning for this will require more attention to the details. If the costs of leisure and travel rise substantially, then inflation will certainly be a major concern.
Looking at persons who are around our age, it appears that most are in situations similar to ours. A few, perhaps 10%, continue to travel, upgrade their cars, and spend lavishly on their homes and lifestyles. For us, the slowing of our lifestyle has more than compensated for any actual inflation.
Overall, I think we can handle a 30% to 40% inflation without making major changes to our plans or lifestyle. At age 65 I would have had a different outlook.