Just installed my first wallet and wanted to test, so I bought £5 worth of BTC from Coinbase, they charged £5.99, I then sent the max amount to my Electrum wallet, amount sent from Coinbase 0.00202070, my wallet received 0.00171727, so I paid £5.99 and have £4.29 in BTC? sound right?
Sounds right. A few factors to consider when looking at your fiat value:
1. Each exchange has its own estimation of BTC value. Coinbase is quite close to the "average price" but often slightly higher.
2. In addition, exchanges charge their own fee. Usually it gets cheaper as you buy more. You actually bought £5 worth of BTC or 0.00202070 BTC. The £0.99 was Coinbase's fee. You can search for other exchanges to buy cheaper BTC. Localbitcoins is normally what I go for.
3. Most exchanges charge a fee for withdrawal, this was deducted from your amount. In this case, Coinbase charged 0.00030343 BTC as a fee (00202070- 0.00171727). Viabtc is currently the only exchange I know with 0 withdrawal fee.
4. BTC value is not fixed against another currency, just like any other currency, except in its own value . So yeah, you never end up with the same fiat value.
So yeah, you lost a substantial chunk of your buy in terms of percentages. But you might have lost a lot less %-wise had you bought 1 BTC.
Welcome to Bitcoin!