There were a total of 54 by-elections along with 31 "double" elections held on 7th May as the election in Mole Valley DC, Holmwoods was deferred following the death of a candidate.
A summary of the by-elections held on 7th May 2015, using the convention that the highest placed candidate in a "double" election wins the annual election and the second placed candidate wins the by-election, is given by:
| Party | Defended | Retained | Gained | Lost | Won | retention rate |
| Conservative | 35 | 34 | 10 | 1 | 44 | 97% |
| Labour | 35 | 29 | 2 | 6 | 31 | 83% |
| Liberal Democrats | 5 | 3 | 2 | 3 | 60% | |
| SNP | 2 | 2 | 1 | 3 | 100% | |
| UKIP | 7 | 1 | 3 | 6 | 4 | 14% |
| Green | 1 | 1 | 0% | |||
| Total | 85 | 69 | 16 | 16 | 85 | 81% |
Overall 16 seats changed hands, some 19% of those contested. This is lower than the ~30% long term proportion but consistent with previous years where a lower proportion do change hands at the time of the May annual elections.
The Conservatives gained 3 seats from Labour, 2 from the Liberal Democrats and 5 from UKIP whilst losing 1 to UKIP
- gained Ipswich: Sprites, Stroud: Easington & Standish and Rossendale: Whitewell from Labour
- gained Somerset: Taunton North and Wiltshire: Chippenham Hardenhuish from Liberal Democrats
- gained Harlow: Great Parndon, Kent: Romney Marsh, Maidstone: Park Wood, Rushmoor: West Heath and Tunbridge Wells: Rusthall from UKIP
- lost Peterborough: Stanground Central to UKIP
Labour gained 1 seat from UKIP and 1 from Green whilst losing 3 to Conservatives, 2 to UKIP and 1 to SNP
- gained Cornwall: Treswithian from UKIP and Watford: Callowland from Greens
- lost Ipswich: Sprites, Stroud: Eastington & Standish and Rossendale: Whitewell to Conservatives
- lost Burnley: Hapton with Park and North East Lincolnshire: East Marsh to UKIP
- lost Fife: Dunfermline South to SNP
-------------------------------------------------------------------------------------------------------------------------------
The convention used for a "double" election is the highest placed candidate wins the annual election, the second candidate wins the by-election.
Conservatives defended 35 seats and retained all apart from the "double" election in Peterborough UA, Stanground Central
- by-elections - 26 all retained
* Barnet LB, Garden Suburb
* Basingstoke & Deane BC, Rooksdown
* Cambridgeshire CC, Whittlesey North
* Camden LB, Hampstead Town
* Cheltenham BC, Battledown
* Cherwell DC, Caversfield
* Cornwall UA, Constantine, Mawnan & Budock
* Craven DC, Barden Fell
* Craven DC, Settle & Ribblebanks
* Craven DC, Upper Wharfedale
* Derbyshire CC, Ashbourne
* Durham UA, Barnard Castle West
* Ealing LB, Northfield
* Hampshire CC, Andover West
* Kensington & Chelsea LB, Stanley
* Leicestershire CC, Narborough & Whetstone
* Newcastle-under-Lyme BC, Clayton
* Norfolk CC, Loddon
* Oxfordshire CC, Witney West & Bampton
* Reigate & Banstead BC, Reigate Hill
* Suffolk CC, Haverhill Cangle
* Surrey CC, Weybridge
* Wandsworth LB, Earlsfield
* Westminster LB, Warwick
* Wiltshire UA, Bromhan, Rowde & Potterne
* Winchester BC, Cheriton & Bishops Sutton
- "double" elections - 2 Conservatives elected in 8 wards
** Birmingham MB, Sutton New Hall
** Bolton MB, Heaton & Lostock
** Hart DC, Hartley Wintney
** Pendle BC, Barrowford
** Redditch BC, West
** Runneymeade BC, Addlestone North
** Southend UA, West Shoebury
** West Oxfordshire DC, Hailey, Minster Lovell & Leafield
** Peterborough UA, Stanground Central: Conservative retain annual election, UKIP gain by-election
Labour defended 35 seats
- by-elections - 18 seats defended, 16 retained and 2 lost
* Bridgend UA, Newcastle
* Durham UA, Ferryhill
* Durham UA, Sherburn
* Durham UA, Willington & Hunwisk
* Enfield LB, Jubilee
* Flintshire UA, Caergwrle
* Greenwich LB, Greenwich West
* Lambeth LB, Prince's
* Merthyr Tydfil UA, Gurnos
* Merthyr Tydfil UA, Town
* Neath Port Talbot UA, Cwmllynfell
* Newham LB, Stratford & New Town
* Southwark LB, Chaucer
* Swansea UA, Crockett
* Swansea UA, Morriston
* Swansea UA, Townhill
* Fife UA, Dunfermline South: SNP gain
* Stroud DC, Eastington & Standish: Conservative gain
- "double" elections - 17 seats defended, 2 Labour elected in 11 wards
** Ipswich BC, St John's
** Kirklees MB, Greenhead
** Knowsley MB, Halewood West
** Liverpool MB, Fazakerley
** Newcastle-upon-Tyne MB, Denton
** Newcastle-upon-Tyne MB, Lemington
** Norwich BC, Miles Cross
** Norwich BC, Sewell
** Rotherham MB, Boston Castle
** Sefton MB, Ravenmeols
** St Helens MB, Haydock
** Bolton MB, Westhoughton & Chew Moor: Conservative gain annual election, Labour retain by-election
** Burnley BC, Hapton with Park: Labour retain annual election, UKIP gain by-election
** Ipswich BC, Sprites: Labour retain annual election, Conservative gain by-election
** North East Lincolnshire UA, East Marsh: Labour retain annual election, UKIP gain by-election
** Rossendale BC, Irwell: Conservative gain annual election, Labour retain by-election
** Rossendale BC, Whitewell: Labour retain annual election, Conservative gain by-election
Liberal Democrat defended 5 by-election seats, retained 3 and lost 2
* Cumbria CC, Cartmel
* Kingston-upon-Thames LB, Grove
* Kingston-upon-Thames LB, Tolworth & Hook Rise
* Somerset CC, Taunton North: Conservative gain
* Wiltshire UA, Chippenham Hardenhuish: Conservative gain
SNP retained both seats defended
* Highlands UA, Nairn
* Perth & Kinross UA, Perth City Centre
UKIP defended 8
3 by-elections with all lost
* Cornwall UA, Camborne Treswithian: Labour gain
* Kent CC, Romney Marsh: Conservative gain
* Maidstone BC, Park Wood: Conservative gain
5 "double" elections
** Harlow BC, Great Parndon: Conservatives retain annual election, gain by-election
** Rushmoor BC, West Heath: UKIP retain annual election, Conservative gain by-election
** Southend UA, St Laurence: Conservative retain annual election, UKIP retain by-election
** Tunbridge Wells BC, Rusthall: Conservatives gain both annual election and by-election
** Mole Valley DC, Holmwoods: deferred election
Green defended 1 "double" election
** Watford BC, Callowland: Labour gain both annual election and by-election
