What is today's price of 15 000 Euro given 15 years ago?
"With no written agreement in place, the ""right"" rate is whatever both parties can agree to. I could argue that I could have invested the money in S&P 500 index funds and made about 9% annually over the last 15 years and the 15,000 would have been over 40,000.  The ""fair"" rate would be whatever rate of return could have been expected from whatever your father would have done with the money otherwise - keep it in a bank account, pay off debt, invest in the market, start a business, whatever.  Your father has the benefit of hindsight to know what would have been a good use of the funds over 15 years. Using the rate of inflation results in effectively a zero-percent loan in real interest terms (meaning no profit was made, just accounting for the time value of money). Both parties need to either decide on an amount or equivalent rate, or decide if squeezing the other for a few thousand Euros is worth the strife." What you are positioning as a loan was not a loan at all. Your father bought something to be delivered in the future. Your aunt does not want to deliver it, so she should buy it back at whatever the current market value is. What is the price that your dad believes her share of the inheritance is currently worth? Is that based on actual appraisals and some sort of objective audit? If so, your aunt doesn't have much of a case. If not, then she could seek an audit to bolster her bargaining position. How much did your aunt benefit from having a place to live for the last 15 years. Was that benefit greater than some larger amount of money at an unknown future date? That's probably why she sold her inheritance 15 years ago. Now that the inheritance looks like it is going to be available soon, she wants to trade back after having enjoyed the use of your father's money. That might be okay, but simply paying back the original sum with inflation, but without interest, doesn't seem fair to your father. She may not be able to afford to give any more than what she is offering, in which case, she might want to consider offering the original sum now and some portion of her inheritance as interest on that original sum. I'm not taking sides in this one. If it were one of my siblings, I'd be inclined to give the benefit of the doubt and take a smaller amount back if I felt that the lesson was learned (and if I felt that he/she would make wise use of my gift to him/her).  I have no idea what your father's current economic situation is, nor am I aware of any other baggage that might influence his feelings about his sister. It's as likely as not that money isn't really what is bothering him, in which case, the amount she repays may have little to do with bridging the divide between them. You might need to ask different questions in the Interpersonal Skills stack if you want to help your father feel better. There's often a legal basis to answer this question. For instance, Austria (guessing from your profile) currently uses a 4% Statutory interest rate. You'll need to dig up not just the actual but also the historical rates. Note that you'll want the non-commercial interest rate - some countries differentiate between loans to businesses and loans to individuals.
You will be liable to pay the tax For the 2017 year of assessment (1 March 2016 - 28 February 2017) if you earned less than R75 000 you will not have to pay any tax The annual budget speach is this week and the new tax rates will be released but most likely that R75 000 will increase to R78 000+- so if you earn less than that tax would not even be applicable on you, Should you earn in a tax year more than R75 000 then would be able to do your own tax return and payments via E-Filling on SARS's website : http://www.sarsefiling.co.za/ But if you earn less than R350 000 then you don't have to submit a tax return, but there is nothing that stops you from submitting one if you feel that you want to. You can use https://www.taxtim.com/za/ to help you with other questions  you might have. You can potentially bring down your tax-able income by showing a loss in capital value of your equipment that you purchased that is now worth less than it was when you initially purchased it, but these are all things you should discuss with a tax practitioner, I am not entirely sure how you will show a loss in capital value as a sole-proprietor, that is what you will be since you are not a company. I have an Italian cafe near me that's run by actual Italians.  There's football games on their TV all the time.  It's very nice, actually, and *never* charges you $15 USD, let alone 15 Euro, for a plate of goddamn pasta. There are so many issues with this graphic.  Plus the timing -- this is a well known and agreed-with position.  This might have been valuable insight or a novel discussion piece 15-20 years ago, but certainly not today.  All it does is provide circle-jerking with logical fallacies using moderately acceptable graphics. I don't recommend Roth for those in the 25% bracket. If you are in the 25% bracket now, I'd suggest you go pretax and as you are planning to be in a lower bracket in a few years, use that bracket to convert. Depositing today at 25% to convert at 15% in a few years puts you that much ahead.  I understand the allure of a Roth heavy strategy. And the fuzzy crystal ball for what the tax code will look like doesn't help. That said, a retiree today who is a few years too young for Social Security will see an Exemption + STD deduction of $10,000, and a 15% bracket ending at $36,250, so $46,250 total with a total tax bill of $4991. A retiree should target $250K-$500K pretax to stay flexible and not miss these low brackets in the future. Inflation is basically this:  Over time, prices go up! I will now address the 3 points you have listed. Suppose over a period of 10 years, prices have doubled.  Now suppose 10 years ago I earned $100 and bought a nice pair of shoes.  Now today because prices have doubled I would have to earn $200 in order to afford the same pair of shoes.  Thus if I want to compare my earnings this year to 10 years ago, I will need to adjust for the price of goods going up.  That is, I could say that my $100 earnings 10 years ago is the same as having earned $200 today, or alternatively I could say that my earnings of $200 today is equivalent to having earned $100 10 years ago. This is a difficult question because a car is a depreciating asset, which means the real value of the car will go down in value over time. Let us suppose that inflation doesn't exist and the car you bought for $100 today will depreciate to $90 after 1 year (a 10% depreciation). But because inflation does exist, and all prices will be 0.5% higher in 1 years time, we can calculate the true selling price of the car 1 in year as follows: 0.5% of $90 = 0.005*90 = $0.45 Therefore the car will be $90 + $0.45 = $90.45 in 1 years time. If inflation is low, then the repayments do not get much easier to pay back over time because wages have not risen by as much.  Similarly the value of your underlying asset will not increase in value by as much. However as compensation, the interest rates on loans are usually lower when inflation is lower. Therefore generally it is better to get a loan in times of high inflation rather than low inflation, however it really depends on how the much the interest rates are relative to the inflation rate. "You will make a profit in nominal dollars (or nominal units of whatever currency you used to buy the token).  Whether you'll make a profit in real dollars depends on inflation, and in practice whether it would be possible to sell your existing tokens to someone else for the new price. Suppose when the price was 50 U (50 ""units"", since you didn't specify a currency), you bought one token.  Today you can either spend 52 U for a token, and get a liter of milk, or you can spend your existing token (for which you paid 50 U) and get a liter of milk.  It looks like you are making a profit of 2 U by spending your token. However, whether that profit is real or illusory depends on what else you could do with the token.  For instance, suppose that, since the price of a token is now 52 U, you will have no trouble finding someone who wants to buy your token from you for 52 U.  If you sell your token for 52 U, you'll still only be able to buy 1 L of milk.  So if you measure your wealth in milk, you have made no profit: in the past you had a token representing 1 L of milk, and today you still have a token representing 1 L of milk. Suppose now that in the past, when a token cost 50 U, a hamburger also cost 50 U.  Suppose further that a hamburger now costs 52 U.  So you can sell your token for 52 U, but that 52 U will still only buy you one hamburger.  So, again, if you measure your wealth in hamburgers, your have made no profit.  In the past, you could have sold your token and bought a hamburger; today, you can still sell your token and buy a hamburger, and you'll have nothing left over, so you have gained nothing. If, on the other hand, the price of a hamburger today is still 50 U, then you call sell your token for 52 U, buy a hamburger for 50 U, and still have 2 U left over.  You have made a profit. What this all goes to show is that, in practice, the idea of ""profit"" depends on the overall economy, and whether you could exchange the currency units you have in your possession for a greater quantity of goods than you could in the past.  Whether this is possible depends on the relative changes in price of various goods.  In other words, if you get your money by selling Product A, and later you buy Product B, you may or may not make a profit depending on how the prices of the two products moved relative to one another. Also, in your hypothetical setup, the ""currency"" (the token) is directly linked to the value of a single good, so you can always at least get 1 L of milk for your token.  Most real currency is not bound to specific goods like your milk token, so it is possible for your currency to lose value in an absolute sense.  For instance, suppose you sell a book for $5.  The $5 is not a ""book token"" and you cannot rely on being able to exchange it for a book in the future; in the future, all books may cost $10, and the prices of all goods may rise similarly, so your currency will actually be worth less no matter how you try to use it.  This could happen with the milk token if the milkman announces that henceforth 1 L of milk will cost 2 tokens; your existing token suddenly loses half its value. In sum, it is easy to calculate whether you made a profit in currency units.  What is harder is to calculate whether you made a profit in ""real terms"" (often referred to as ""real dollars"" or ""inflation-adjusted dollars"", or the equivalent in your favorite currency).  The reason this is hard is because the idea of ""real dollars"" is fundamentally linked to the possibility of exchanging currency for goods (and services), and so it depends what goods you're buying.  Inflation statistics published by governments and the like use a ""basket"" of goods to approximate the overall price movements in the economy as a whole." I would never consider such an offer. As has already been mentioned, there are likely to be hidden costs and the future is never certain. If you feel that you are missing out, then negociate a lower purchase price now. People often forget that something is only worth what someone is willing to pay for it. With any significant purchase it's always worth bargaining. "As others have noted, your definition of ""market price"" is a bit loose.  Really whatever price you get becomes the current market price.  What you usually get quoted are the current best bid and ask with the last transaction price.  For stocks that don't trade much, the last transaction price may not be representative of the current market value. Your question included regulation (""standards bureau""), and I don't think the current answers are addressing that.  In the US, the Securities and Exchange Commission (SEC) provides some regulation regarding execution price.  It goes by the designation Regulation NMS, and, very roughly, it says that each transaction has to take the best available price at the time that it is executed.  There are some subtleties, but that's the gist of it. No regulation ensures that there will be a counterparty to any transaction that you want to make.  It could happen, for example, that you have shares of some company that you're never able to sell because no one wants them. (BitCoin is the same in this regard.  There is a currently a market for BitCoin, but there's no regulation that ensures there will be a market for it tomorrow.) Outside of the US, I don't know what regulation, if any, exists."