The default answer
You are still employed by the original employer for every day of the notice period. Every obligation in your contract continues to apply. Most UK professional contracts contain an exclusivity clause that prohibits working for any other employer during your employment. Two full-time jobs at once breaches this clause.
Even without an explicit exclusivity clause, the duty of good faith implied into every UK employment contract generally prevents you from taking on conflicting parallel employment.
So the headline answer for almost everyone is: align the dates. Start the new role on the day after the old contract ends.
Working out your final working day
Count the contractual notice from the date your written resignation reached your employer. The notice period calculator handles the date arithmetic for any notice length. The final working day calculator gives you the same answer with weekend and bank holiday rollback options.
The next-day-start pattern is the cleanest and most common. Your last working day at the old employer is (say) Friday 30 May; you start the new role on Monday 2 June. No overlap, no gap, no contractual conflict.
If the new employer needs you sooner
A common scenario. The new employer would like you to start in three weeks; your existing contract has a two- or three-month notice. Three options:
1. Negotiate a shorter notice. Many UK employers will agree to a shorter notice if a credible handover is in place and the next employer needs you. The conversation is professional, the answer is often yes, and the saved time benefits the existing employer too (they stop paying you sooner).
The way to ask: a short, specific written conversation with your line manager and HR. Confirm what you have completed in the handover, propose a specific shorter date, and ask for their agreement in writing. The can I leave before my notice ends? guide covers the mechanics.
2. PILON. If your contract has a PILON (payment in lieu of notice) clause, the employer can end the contract immediately and pay the notice period as a lump sum. Some employers will do this on request even without a clause if it suits both sides. The PILON calculator models the gross figure. See PILON explained for the rules.
3. Later start at the new employer. Most new employers accept a later start if the candidate they want is otherwise unavailable. The conversation: confirm the earliest realistic date based on your contractual notice, explain the handover work that remains, and propose a specific date that works on both sides.
The garden-leave scenario
If your employer puts you on garden leave (you remain employed and paid but do not come to work), you are still bound by all contractual obligations including exclusivity. You cannot start a new job until the garden leave ends.
Garden leave often runs the full notice period for senior or competitor-sensitive roles. It is financially fine (you continue to be paid) but the start date for the next role is delayed accordingly. See garden leave explained and the garden leave calculator.
The new employer’s perspective
Reputable UK employers will not knowingly ask you to breach your existing contract. Most ask in the offer process when you can start, and accept the answer based on your notice period. A new employer who pushes you to start before your contractual notice ends is signalling that they will accept short cuts in other situations too. That is worth noting.
Where there is a genuine business reason for the new employer to need you sooner (a project starting, a team transition), they will usually help with arranging it through PILON or accepting a slightly later partial start (one day a week before full-time, for example) where the contractual position allows.
Evening or weekend work in another job
Doing a few hours of evening or weekend work in an unrelated field is a different question. Two factors matter:
- Exclusivity clause: many professional contracts ban outside work even if it is unrelated. Check yours.
- Sector overlap: if the evening work overlaps with the current employer’s customers, suppliers, confidential information or competing market, it is a problem regardless of the time of day.
For the broader picture, see can I work during my notice period?
What happens if you start the new job anyway
Practical consequences:
- The original employer can terminate the existing contract for breach. PILON, bonus, commission or other notice-period payments are at risk.
- The original employer can claim damages for losses caused. Common claim: lost productivity, cost of finding cover, customer losses if you took client information with you.
- If your contract has restrictive covenants, the original employer can seek an injunction to prevent you continuing in the new role. Injunctions are rare but real for senior or competitor-sensitive departures.
- Reference damage. A confirmed breach of contract sits in your HR file and is hard to recover from in subsequent applications.
- For regulated professionals (lawyers, accountants, doctors, nurses, financial services), potential professional-conduct consequences.
If you have already signed somewhere else
If you signed an offer that has you starting before your notice ends and you have only just realised the conflict, the practical fix is the same. Confirm your contractual notice end date. Tell the new employer the earliest realistic start (the day after your notice ends). They will usually accept it. If they will not, discuss with your existing employer whether a shorter notice or PILON works.
Trying to do both at once is the worst outcome. The existing employer almost always finds out (LinkedIn, mutual connections, social media), and the new employer discovers they hired someone in breach of contract.
Useful calculators
Related guides
- Notice period rights UK — the pillar guide.
- Can I leave before my notice ends?
- Can I work during my notice period?
- Working for a competitor during notice period
- PILON explained
- Garden leave explained
- Employment rights hub
Frequently asked questions
- Can I legally start a new full-time job while still in my notice period?
- Usually no. Two full-time roles at once is almost always a breach of one or both contracts because of exclusivity, non-compete and conflict-of-interest clauses. The standard pattern is to align the dates so the new role starts on the day after the old contract ends. If the new employer needs you sooner, the route is a negotiated shorter notice or PILON.
- What if my employer agrees to me starting the new job early?
- Then it is allowed for the period they have agreed. Get the agreement in writing from your line manager or HR specifying the date you stop working for them and any conditions. The agreement amounts to a mutual shortening of your notice period. From the agreed end date you are no longer employed by the original employer.
- Can I do the new job in the evenings while serving notice in the daytime?
- Subject to the same contractual constraints as any second job. The exclusivity, confidentiality, non-compete and good-faith obligations all apply. If the new job is in an unrelated sector with no overlap, evening work might be acceptable. If it is in the same sector or for a competitor, almost certainly not. Read the contract and ask if uncertain.
- How do I align the two dates cleanly?
- Three steps. Confirm the final working day on the existing contract (date you handed in notice plus contractual notice period). Confirm the new employer's expected start date. If they overlap, ask the existing employer for a shorter notice or PILON, and ask the new employer if a later start is possible. Most situations resolve in the first round of conversations.
General information about UK contractual notice. Specifics depend on your contract. For your situation, contact ACAS or an employment-law solicitor.