It's a bit complicated.
You see, I went to the garage to fill up our little car. Sainsbury's for unleaded are charging £1.27.9 a litre, so it should be easy to know what it costs. I filled up and it came to 33.02 litres, so using my 10p a litre voucher from a £60 supermarket shop earlier in the week, I got £3.30 off. That gets us to £42.23 - £3.30 = £38.93.
Ah, but there are Nectar points earned on the petrol - 33 of them. If I save them and use them, they're effectively worth 0.5p each and I got a double Nectar points due to a special coupon from my last purchase in the supermarket. So I now have a potential 33p to spend in the future. Get excited!
But that's still not it, because I paid on my Nationwide credit card, which gives me 0.5% cash back on purchases each month, redeemable at the end of the year. So that's, er, about 19.5 pence.
So if I claim my Nectar points and allow for what gets docked off my december credit card bill, my petrol actually cost £38.93 - £0.33 - £0.19½. I make that £38.40½.
That's great, but am I the only one thinking it could be simpler?