On paper, 26.2 looks an inoffensive number. On foot, this distance in miles can seem the harshest of ordeals - especially if you're running and wearing fancy dress.
Happily, the money it raises for charity makes all the agony worthwhile. In one week's time, some 30,000 runners will adopt this spirit and push themselves to the limit as London plays host to one of the world's most famous marathons.
The event is also one of the biggest events in the UK fundraising calendar, bringing in some £36m in total last year.
While next Sunday's runners will be shedding physical pounds to raise financial ones, there are other, less strenuous ways to help charities. A click of a computer mouse is particularly quick and convenient. In 2004, internet donations via the Charities Aid Foundation (CAF) more than doubled to £6.8m, says the organisation's spokeswoman, Vicki Pulman.
"Many people used online giving for the first time when donating to the tsunami appeal, because it enabled them to respond immediately," she says.
However you choose to be charitable, make sure you make your donation work as hard as possible by handing it over in the most tax-efficient way. More than two-thirds of us give regularly to charity but only one in three do so in a manner that lets the charity reclaim tax, according to the CAF, which estimates that £700m a year is lost to the Treasury as a result.
Tax-efficient generosity may require a bit more effort than simply throwing money in a collecting bucket, but it will make far more of an impact. Popular ways to make the most of donations are outlined below.
You must be a taxpayer to take advantage of this scheme, by which every pound you give to your chosen charity secures another 28p from the taxman.
Look for the Gift Aid box to tick when you make your donation on the back of a postal appeal or an advert in a newspaper. If there isn't one, ask the charity for a form or print one off from the Inland Revenue's website (see below).
Higher-rate taxpayers can claim an extra 18 per cent tax relief on their original donation when filling in their self-assessment forms.
One of the easiest ways to make regular tax-efficient charitable contributions is via your payslip. "Payroll giving" donations are deducted from your pre-tax pay packet by your employer, which must be signed up to a payroll charity scheme such as CAF's Give As You Earn. You simply nominate your charities and say how much you want to give; your choice can be changed at any time.
More than five million workers now give in this way, according to Ms Pulman, and UK payroll giving surged from £27m in the 1999-2000 tax year to £91m in 2003-04. If your company is not enrolled, ask your personnel department about signing up. New government grants are on offer to encourage more employers to do this.
Do you have unwanted shares, land or property to give away? Hand these over to a charity and you'll be exempt from capital gains tax and able to claim income tax relief at the same time.
For example, a basic-rate taxpayer making a gift of £5,000 worth of listed shares could deduct this sum from their overall income tax bill.
Alternatively, if you have inherited very small shareholdings, you could give them to a donation scheme such as ShareGift. They will then be pooled with donations from others before being sold to raise money.
Donations made as part of a will are among the most valuable sources of income for charities. They are paid out of an estate before inheritance tax (payable on any sum above a £275,000 threshold) is deducted, cutting the total tax paid on the estate.
Many people leave a sum directly to a particular charity but an alternative is to donate the "residue" - any money left after everything else has been settled.
"In the past, fundraisers had to trawl around the office asking colleagues for money," says James Grieve, spokesman for the fundraising website www.justgiving.com, an official partner of this year's London Marathon. "Now, with [increased use of the internet] and Gift Aid, giving tax efficiently has been simplified.
"While people tend to hand you £5 if you ask around the office, the average online donation is £35."
Justgiving.com lets individuals build their own websites for charitable fundraising, and donors can click the Gift Aid box. However, it does levy a 5 per cent transaction fee on donations, to cover running costs.
So, if you pledged £100 via Gift Aid at justgiving.com, your charity would reclaim an extra £28 from the Inland Revenue, but would receive £123 after a £5 deduction by the website.
HERE I GO AGAIN
After the pain of the 2004 marathon, I promised never again to run 26.2 miles, but in a moment of weakness I crumpled and agreed to do it all over again this year.
Buffeted by wind, drenched by rain and even dazzled by snow, I've been pounding the Thames towpath for the past four months. I won't pretend training has been easy.
But it's been more bearable as I know that I'm running for the Samaritans, and that - with the aid of a fundraising page at www.justgiving.com/run-esther-run - I've made nearly £3,000 for the cause. I've been amazed by people's generosity, boosted by Gift Aid to far exceed my original fundraising goals.Reuse content