Here’s a quick way of working out how much your entire portfolio costs to run at the fund level. Simply take each fund in your portfolio and…

Multiply the fund’s Ongoing Charge Figure (OCF) by the percentage of your portfolio that’s allocated to the fund.

This gives you the weighted OCF of each fund in your portfolio.

For example, here’s the total OCF for Monevator’s Slow and Steady portfolio:

 Index fund Allocation (%) OCF (%) Weighted OCF (%) BlackRock US Equity Tracker Fund D 25 0.18 0.25 x 0.18 = 0.045 BlackRock Continental European Equity Tracker Fund D 12 0.18 0.12 x 0.18 = 0.0216 Vanguard FTSE UK Equity Index Fund 15 0.15 0.15 x 0.15 = 0.0225 BlackRock Japan Equity Tracker Fund D 7 0.18 0.07 x 0.18 = 0.0126 BlackRock Pacific ex Japan Equity Tracker Fund D 7 0.24 0.07 x 0.24 = 0.0168 BlackRock Emerging Markets Equity Tracker Fund D 10 0.28 0.1 x 0.28 = 0.028 Vanguard UK Government Bond Fund 24 0.15 0.24 x 0.15 = 0.036 Total portfolio OCF – – 0.18%

Source for OCFs: Fund factsheets.

The actual OCF of your entire portfolio may be quite a jolt. We tend to overestimate the importance of the cheapest funds even if they only account for a sliver of the whole cheese.

If you’re tempted to risk a switch to the new fund on the block, it’s instructive to find out just how little it may move your dial. The risk of losing money due to a spike in the market while your cash is on the sidelines may well outweigh any marginal cost shaving.

### What’s that in real money?

The real value in knowing your portfolio’s total OCF is that you can now work out how much it actually costs in pounds and pence.

Just multiply the market value of your fund by its total OCF and you’ll have a rough idea of what you’re paying out.

Continuing with our Slow and Steady example, our little portfolio had a market value around £11,400 the last time I looked. Its total OCF of 0.1825% means that it will incur annual fund fees in the region of:

£11,400 x 0.001825 = £20.80

I know! We’re high rollers around here.

Obviously the portfolio’s market value will fluctuate and more cash will be poured in, but that figure let’s us know what ballpark we’re playing in.

Note: The cost represented by the OCF doesn’t include platform fees, dealing fees, tracking error, and any spreads that may be leeching away our returns.

Now, it’s not unknown for passive investors of my geeky disposition to get a little obsessive over costs. That’s one of the few things we know we can control.

So it’s instructive to remember that if the Slow and Steady portfolio was 50% more expensive then that would amount to about £10 a year extra on the bill. In other words, the price of a few drinks in the pub.

Anyone who’s fallen for media scare stories along the lines of “eating jam can increase your chances of contracting leprosy by 30%” when the incidence of the original illness is absolutely minimal will understand how misleading percentages can be when not rooted in reality.

Sure, the money gets more serious the larger your portfolio. And small pots undoubtedly benefit from careful husbandry.

But by calculating the cost of your entire portfolio, you can silence any worries that you may be leaking cash like a Premier League footballer in a strip club.