We also need to know when he opened it.
Annual interest = 5760 x 0.0175.
You then need to adjust that according to the number (or fraction) of years it was in place
For the pedants:
23rd April - 20th March = 331 days.
Assume interest is paid daily and is compounded.
Daily interest rate = 365th root of 1.0175 = 1.000047532 (ie a daily interest of 0.0047532%)
Total accrued after 331 days = 331st power of 1.000047532 = 1.015857008
Multiply this by original investment of £5760 - giving a total return of £5851.34.
Interest gained = £5851.34 - £5760.00 = £91.34
Thanks Gizmonster. Maybe one of the days should be excluded though if the investment or closure occurred part way through the day. And maybe interest didn't accrue for the first few days until the funds had cleared. Maybe the figure is as low as £90
Best one I found recently is with Coventry Building Society, fixed at 2.75% for 2 years (although I think they've recently changed it to 3 years). If you withdraw early, the penalty is only 120 days interest (others are usually 180 days), so even if you withdraw early, it still beats most other ISAs on offer at the mo :)
@ boxtops - approx 12 months ago I managed to get an ISA fixed at 3% for 3 years - the only problem is, I can't add to it, so I'm constantly looking for new deals each year :(