How to clean windows without streaks

To clean windows without streaks, wash them when the glass is in shade, using a bucket of warm water with a small squeeze of dish soap. Scrub with a sponge or strip washer, pull the water off with a squeegee, and wipe the blade dry after every stroke. Finish the edges with a dry microfiber cloth.

What you need

A bucket of warm water with a small squeeze of dish soap, or a spray bottle of half white vinegar, half water
A squeegee with a sharp, undamaged rubber blade
A sponge, or a strip washer (the fluffy T-bar sleeve window cleaners use)
Two or three clean, dry microfiber cloths or a lint-free towel
An old towel for the sill

Andersen's window cleaning guide gives both mixes: roughly a 10-second squeeze of dish soap in 2 to 3 gallons of water, or equal parts distilled white vinegar and water in a spray bottle. The soap mix is better for dirty outside glass. Vinegar is handy for inside glass that's only smudged.

How to clean windows without streaks, step by step

Pick a cloudy day, or do each window when it's in shade. Andersen's reason is simple: the sun dries the solution faster than you can wipe it off, and dried solution means streaks.
Dust the frame and sill first, and brush off any cobwebs. Otherwise the first wet pass turns that dust into mud on the glass.
Wet the glass with the sponge or strip washer and scrub the whole pane, corners included. Don't be shy with the water. A properly wet window is easier to squeegee clean than a damp one.
Dry a 1-inch strip along the top of the glass with a cloth so the squeegee has a clean place to start.
Pull the squeegee down from that dry strip in one smooth stroke, overlapping each stroke by an inch or so. On big panes, you can also work in a continuous S-shape from top to bottom without lifting the blade.
Wipe the squeegee blade with a dry cloth after every single stroke. Skipping this is a classic cause of streaks.
Run a dry microfiber cloth around the edges of the pane where the squeegee can't reach, and wipe up the puddle on the sill.
Check the glass from a different angle once it's dry. A useful trick: squeegee the inside with horizontal strokes and the outside with vertical ones. Then the direction of any leftover streak tells you which side it's on.

Why your windows still streak

The sun is on the glass. The solution flash-dries before you remove it.
Too much soap or cleaner. Andersen's ratio is a short squeeze in a couple of gallons of water. More than that leaves a film.
The squeegee blade is nicked, worn or dirty. Rubber edges get chewed up quickly. Replace the blade when it stops leaving a clean line.
The cloth is linty or was washed with fabric softener. Softener coats the fibers and smears. See how to wash microfiber cloths.
Dirty water. Change the bucket once it looks cloudy.
Haze that won't wipe off may be on the inside of a double-pane unit. If it's fogged between the panes, the seal has failed and no amount of cleaning will reach it. Contact the window maker or a glazier.

Can you use a razor blade on windows?

Not on modern windows unless the manufacturer says you can. Andersen warns against razor blades and abrasive cleaners or solvents because they can scratch or damage the glass. Many newer windows also have coatings on the glass, such as low-E coatings, and Andersen says neither toothpaste nor mineral spirits should be used on windows with special coatings like its HeatLock glass. For paint specks or sticker glue, soak the spot with your soapy water and try a plastic scraper or your fingernail first.

Cleaning frames, sills and tracks

Glass is only part of it. While you're there:

Vacuum the window tracks with a crevice tool. Dead bugs and grit collect in the corners.
Wipe the tracks and sills with a damp cloth. A cotton swab or an old toothbrush reaches the corners.
Clear the small weep holes at the bottom of the frame, if your windows have them. They let rainwater drain out of the track.
Wipe vinyl or painted frames with the same soapy water. Don't use harsh or abrasive cleaners on them either.

How often should you clean windows?

Andersen recommends washing windows twice a year, ideally in spring and fall. That's a reasonable baseline for the outside glass. The inside usually needs more:

Window	How often
Outside glass	Twice a year, spring and fall
Inside glass, most rooms	Every 2 to 3 months, or when smudged
Kitchen windows	Monthly, since cooking grease builds a film
Windows near the coast or a busy road	Outside every 3 to 4 months
Glass doors and windows kids or pets can reach	Weekly spot clean

Doing high windows safely

Many double-hung windows have sashes that tilt in so you can clean the outside from indoors. Check the manual before you try, and stop if a sash doesn't move the way you expect. For upper-floor exterior glass you can't reach from the ground or from inside, hire a window cleaner with the right equipment. Leaning out of an upstairs window or stretching off a ladder to reach one more pane isn't worth the risk.

Do the screens and blinds first

Dust the blinds and take out the window screens before you wash the glass. Otherwise you'll knock dust onto clean windows, or put dirty screens back over them. Twice a year is easy to forget, so a ChoreLists.com reminder in spring and fall does the remembering for you.