Time is money. We all know that. But do you know how much your time is worth? I recently helped a self-employed client work out this cost, and thought I’d share the process.

The starting point is to work out how much it costs to “keep you alive” each month. This should include your rent or mortgage, your utility costs, average food bill, travel costs, a contribution to a small annual holiday, and a little contingency “just in case”. Let’s say, for example, that this amounts to £1,200.

You now multiply this cost by 12 to get your annual cost: £14,400.

Assuming an average working year of 220 days, you need to earn just over £65 every day to stand still. However, that’s after paying tax. So your gross earnings would need to be in the region of £80 per day.

So assuming an 8 hour day, it costs you £10 an hour to sit still.

It might not sound much, but every hour you don’t earn means you have to earn more in the other hours. Let’s say you only earn in 60% of the time. You need to charge about £135 a day, or £17 per hour.

So when you sit down to read or do something that you are not being paid for, ask yourself, is it worth £17 per hour?

One of the oldest concepts in international economics is the theory of purchasing-power parity (PPP). PPP argues that, in the long run, exchange rates should move towards levels that would equalise the prices of an identical basket of goods and services in any two countries.

The Economist uses just one item: the Big Mac.

If a Big Mac costs £2.50 in the UK, at today’s exchange rate (£1 = $1.46677), a Big Mac in the US should cost $3.67.

If it costs more than $3.67 then the PPP concept suggests that the pound is overvalued (or the dollar is undervalued). The consequence of this is that, all things being equal, either the pound will go up, or the dollar will fall.

Too simple? Possibly, but as a measurement of exchange rates, Big Maconomics has endured.

Sometimes I think we make life too complicated and not enough fun.

There is some confusion about the implications of the change in VAT.

First off, the potential saving is 2.1%, not 2.5%. This is because the saving relates to the VAT, not the whole value.

So a widget that sold for £11.75 on 30 November should cost £11.50 on 1 December. The saving is therefore 25p. 25p as a percentage of £11.75 is 2.128% (call it 2.1%), not 2.5%.

Hardly something to write home about and I have my eyes peeled to find anyone who is actually passing this saving onto the customer. Anyone found a bargain yet?