Adjusting a value for inflation each month using rolling 12-monthly inflation figures
In the style of the Bank of England's Inflation Calculator, you can do the calculation like so. The third column is an index made from the inflation figures and the forth column shows the inflation-adjusted values.  Using the index to calculate the difference in costs, for example: The formulas used to produce the table above are shown below. "The actual increase in the cost of living for one month over the previous month cannot be calculated from the annualized increase in cost over the entire previous year. Consider the hypothetical case of a very stable economy, where prices stay constant for decades.  Nevertheless, the authorities issue monthly statements, reporting that the change in the cost of living, for the last month, year over year, is 0.00%.  Then they go back to sleep for another month. Then, something happens, say in August, 2001.  It causes a permanent large increase in the cost of many parts of the cost of living components. So, in September, the authorities announce that the cost of living for the end of August, 2001, compared to August a year ago, was up 10%. Great consternation results.  Politicians pontificate, unions agitate on behalf of their members, etc... The economy returns to its customary behavior, except for that one-time permanent increase from August, 2001.  So for the next eleven months, each month, the authorities compare the previous months prices to the prices from exactly a year ago, and announce that inflation, year over year, is still 10%.   Finally, we reach September, 2002.  The authorities look at prices for the end of August, 2002, and compare them to the prices from the end of August, 2001 (post ""event"").  Wonder of wonders, the inflation rate is back to 0.00%!!  Absolutely nothing happened in August 2002, yet the rate of inflation dropped from 10% to 0%."
The key to understanding a mortgage is to look at an amortization schedule.  Put in 100k, 4.5% interest, 30 years, 360 monthly payments and look at the results.  You should get roughly 507 monthly P&I payment.  Amortization is only the loan portion, escrow for taxes and insurance and additional payments for PMI are extra. You'll get a list of all the payments to match the numbers you enter.  These won't exactly match what you really get in a mortgage, but they're close enough to demonstrate the way amortization works, and to plan a budget.  For those terms, with equal monthly payments, you'll start paying 74% interest from the first payment.  Each payment thereafter, that percentage drops. The way this is all calculated is through the time value of money equations.  https://en.wikipedia.org/wiki/Time_value_of_money.  Read slowly, understand how the equations work, then look at the formula for Repeating Payment and Present Value.  That is used to find the monthly payment.   You can validate that the formula works by using their answer and making a spreadsheet that has these columns:  Previous balance, payment, interest, new balance.  Each line represents a month.  Calculate interest as previous balance * APR/12.  Calculate new balance as previous balance minus payment plus interest. Work through all this for a 1 year loan and you will understand a lot better. You shouldn't. The Dow has gained 7% annually on average since October 1915(inflation-adjusted). It has also lost 73% of its inflation-adjusted value from 1966 to 1982 meaning that it would have lost you 4.5% annually for 16 years. Furthermore, past performance is not indicative of future results. If stock markets keep performing like they have for the past 100 years, you can expect there will be a point within the next 60-or-so years your stocks will be higher in value than they were when you bought them. With funds you are paying the people managing them which means you are guaranteed to have pyramiding losses that your gains will have to offset. In your case, you are betting with no fundamental knowledge that S&P will be higher than now whenever you need the money which is not even supported by the above assumption. Dollar averaging just means you will be placing many bets which will reduce your expected losses(and your expected gains) when compared to just buying $100K worth of S&P right now. Whatever you invest in, and whatever your time-frame, don't gamble. If you can't say this company(ies) will be $X more valuable than now in X months with probability > Y, then you shouldn't be investing in it. Nobody ever made money by losing money. There are also safer investments than the stock market, like treasury bonds, even if the returns are lousy. We need to be careful what we are talking about here. Inflation on a economy-level scale at an expected rate will not change consumer habits because the price increase is manageable. You have to realize that prices are not increasing in isolation: wages will have to rise along too.  High inflation that is expected will increase consumption of durable goods, as people attempt to 'get rid of their money' before the price changes on them. A good example of this was post-WWI germany, where hyperinflation was so bad that offices began to pay their employees twice daily, so they could adjust their wages, and so that their employees could go out during lunch and after work to buy something with the money before the price changed on them. Unexpected inflation may cause a temporary dip in spending until wages adjust, however consumers still need to buy, so they will likely push for higher wages, leading to consumption to stay about level. There is another effect to inflation as well: People who have savings will have their savings eroded over time if the economy is inflationary. To preserve their wealth, they will invest it. In a deflationary environment, money will increase in value simply by being hoarded, so they will be less willing to invest it. Deflation also increases the cost of interest on a loan, while inflation decreases it. So the overall effect is for an increase in spending under inflation, and a decrease under deflation. The person you have quoted is quite wrong. Price increases in a particular sector will cause consumer spending to decrease but this is a bad example, as it is not inflation, but rather a supply/demand problem of a particular consumer good. They are applying a micro-economic model (price increases of a single good) to a macroeconomic problem (price increases in the entire economy) when price increases at a global scale have the opposite effects. A good theoretical test of this is: what would happen if everyone in the US suddenly had twice as much money? (Ignoring international trade, of course). The answer: prices will double, and nothing else will change. The reason is, people will have more money to spend, but will require more money for their services, so in the end it all cancels out. "The short answer is the annualised volatility over twenty years should be pretty much the same as the annualised volatility over five years. For independent, identically distributed returns the volatility scales proportionally. So for any number of monthly returns T, setting the annualization factor m = 12 annualises the volatility.  It should be the same for all time scales.  However, note the discussion here: https://quant.stackexchange.com/a/7496/7178 Scaling volatility [like this] only is mathematically correct when the   underlying price model is driven by Geometric Brownian motion which   implies that prices are log normally distributed and returns are   normally distributed. Particularly the comment: ""its a well known fact that volatility is overestimated when scaled over long periods of time without a change of model to estimate such ""long-term"" volatility."" Now, a demonstration.  I have modelled 12,000 monthly returns with mean = 3% and standard deviation = 2, so the annualised volatility should be Sqrt(12) * 2 = 6.9282.   Calculating annualised volatility for return sequences of various lengths (3, 6, 12, 60 months etc.) reveals an inaccuracy for shorter sequences.  The five-year sequence average got closest to the theoretically expected figure (6.9282), and, as the commenter noted ""volatility is [slightly] overestimated when scaled over long periods of time"". Annualised volatility for varying return sequence lengths  Edit re. comment Reinvesting returns does not affect the volatility much.  For instance, comparing some data I have handy, the Dow Jones Industrial Average Capital Returns (CR) versus Net Returns (NR).  The return differences are somewhat smoothed, 0.1% each month, 0.25% every third month.  More erratic dividend reinvestment would increase the volatility." Line one shows your 1M, a return with a given rate, and year end withdrawal starting at 25,000.  So Line 2 starts with that balance, applies the rate again, and shows the higher withdrawal, by 3%/yr.  In Column one, I show the cumulative effect of the 3% inflation, and the last number in this column is the final balance (903K) but divided by the cumulative inflation.  To summarize - if you simply get the return of inflation, and start by spending just that amount, you'll find that after 20 years, you have half your real value.  The 1.029 is a trial and error method, as I don't know how a finance calculator would handle such a payment flow. I can load the sheet somewhere if you'd like.  Note: This is not exactly what the OP was looking for. If the concept is useful, I'll let it stand. If not, downvotes are welcome and I'll delete. "I was afraid of this. If you are using 12 P/Y and 12 C/Y, then your interest rate should not be divided by 12. Also, you should use ""END"" as this means monthly payments are made at the end of the month - a usual default." But has inflation went up ? The only reason jobs would be lost would be if the cities economy couldn't absorb the inflation .  Since you are now increasing the incomes of every one at the bottom , the city will likely be able to absorb the inflation . The question really is have the people at the bottom increased there spending power over all  and have there been winners and losers for example maybe servers are doing better but retirees and others on a fixed income worse . "The graphing tools within Yahoo offer a decent level of adjustment. You can easily choose start and end years, and 2 or more symbols to compare.  I caution you. From Jan 1980 through Dec 2011, the S&P would have grown $1 to $29.02, (See Moneychimp) but, the index went up from 107.94 to 1257.60, growing a dollar to only $11.65. The index, and therefore the charts, do not include dividends. So long term analysis will yield false results if this isn't accounted for.  EDIT  - From the type of question this is, I'd suggest you might be interested in a book titled ""Stock Market Logic."" If memory serves me, it offered up patterns like you suggest, seasonal, relations to Presidential cycle, etc. I don't judge these approaches, I just recall this book exists from seeing it about 20 years back."